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Michael Otu
Michael Otu

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Introduction to SQL using SQLite: Data Manipulation

#sql #api #beginners #node

Objectives

  • DROP TABLE
  • INSERT
  • SELECT
  • FILTERS
  • FUNCTIONS
  • UPDATE
  • DELETE

Introduction

We discussed that, to create a table for the object,

const profile = {
    name: "John Doe",
    "date of birth": "2000-12-25",
    profession: "Software Engineer",
    "number of pets": 2,
    "weight of protein in grams": 12.5,
    "has a job": true,
};
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We would have to analyse it and design a table that meets the requirements of our system, building on the knowledge we already have in JavaScript.

property JS SQL Constraint
name string TEXT NOT NULL
date of birth Date TEXT
profession string TEXT DEFAULT ''
number of pets number INTEGER DEFAULT 0
weight of protein in grams number INTEGER DEFAULT 0
has a job boolean INTEGER DEFAULT 0

This would logically boil down to something like:

CREATE TABLE "profile" (
    "id" INTEGER PRIMARY KEY AUTOINCREMENT,
    "name" TEXT NOT NULL,
    "dateOfBirth" TEXT,
    "profession" TEXT DEFAULT '',
    "numberOfPets" INTEGER DEFAULT 0,
    "weightOfProteinInGrams" INTEGER DEFAULT 0,
    "hasJob" INTEGER DEFAULT 0
);
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In this section, we are going to focus on data manipulation, CRUD. Check out Request And Response, where we discussed CRUD and Basic Crud Api With Express, where we started building a CRUD application.

We will borrow a table here.

CRUD HTTP VERBS SQL
CREATE POST INSERT
READ READ SELECT
UPDATE PUT UPDATE
DELETE DELETE DELETE

DROP TABLE

First things first, if you can create, you should "un"-create. To "un"-create a table, we have to "drop" it. General syntax is:

DROP TABLE <TABLE_NAME>;
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For the profile table or human table, we can drop it by executing the script, DROP TABLE "profile"; OR DROP TABLE "human";.

; signifies the end of the script (that line or snippet).

Know that this action is not reversible in most situations.

INSERT

Syntax for INSERT is generally,

INSERT INTO <TABLE_NAME> (<column1>,<column2>,...,<columnN>,) VALUES (<value1>, <value2>, ...,<valueN>);
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This is the snippet for creating the "human" table.

CREATE TABLE "human" (
    "id" INTEGER PRIMARY KEY AUTOINCREMENT,
    "firstName" TEXT NOT NULL,
    "lastName" TEXT NOT NULL,
    "socialSecurityNumber" TEXT NOT NULL UNIQUE,
    "email" TEXT NOT NULL UNIQUE,
    "dateOfBirth" TEXT,
    "hasPet" INTEGER DEFAULT 0,
    "numberOfCars" INTEGER DEFAULT 0
);
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Let's create a row for John Doe with SSN, 123-45-6789, who has no pet and no car, born on 14th of March, 1990, with johndoe1990@gmail.com as email.

INSERT INTO "human"
 ("firstName", "lastName", "socialSecurityNumber", "email", "dateOfBirth", "hasPet", "numberOfCars")
VALUES
 ('John', 'Doe', '123-45-6789', 'johndoe1990@gmail.com', '1990-03-14', 0, 0);
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This will create a unique row for John Doe with 123-45-6789 as SSN.

Do you think we can create another row with the same details? Try it.

You should get UNIQUE constraint failed: human.email.

Create two more "human" records.

We can create more rows at once, bulk insert, by

INSERT INTO <TABLE_NAME>
 (<column1>,<column2>,...,<columnN>,)
VALUES
 (<value1>, <value2>, ...,<valueN>),
 (<value1>, <value2>, ...,<valueN>),
 (<value1>, <value2>, ...,<valueN>),
 (<value1>, <value2>, ...,<valueN>),
 ...
 (<value1>, <value2>, ...,<valueN>);
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SELECT

The syntax for a SELECT statement is:

SELECT <FIELDS TO SELECT> FROM <TABLE NAME>;
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So let's say we want the firstName and lastName columns from the human table, then will do

SELECT "firstName", "lastName" FROM "human";
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This is how my output looks from the terminal.

user$ sqlite3 app.sqlite
SQLite version 3.43.2 2023-10-10 13:08:14
Enter ".help" for usage hints.
sqlite> SELECT "firstName", "lastName" FROM "human";
John|Doe
Anne|Ali
Gifty|Doe
Idris|Johnson
sqlite>
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In beekeeper-studio, it looks "pretty"







For the above output, these are the inserts.

INSERT INTO "human"
 ("firstName", "lastName", "socialSecurityNumber", "email", "dateOfBirth", "hasPet", "numberOfCars")
VALUES
 ('Anne', 'Ali', '123-45-6790', 'alianne@gmail.com', '1995-12-21', 0, 1),
 ('Gifty', 'Doe', '123-45-6791', 'giftydoe@gmail.com', '1995-01-11', 1, 0),
 ('Idris', 'Johnson', '123-45-6792', 'johnidrisson@gmail.com', '1992-06-30', 0, 2);
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When selecting a column for display, you have to account for the use of the column. When the client doesn't have that column, don't send it.

There is another way to select all the columns from a table, which is useful at times. This can be done by replacing all the with *, an asterisk.

SELECT * FROM "human";
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The response is quite similar, but with all the fields this time.



Selecting first and last name using beekeeper studio



SQLite can be configured to look "pretty". Check out sqlite-dot-commands

We can use the column mode

sqlite> .mode column
sqlite> SELECT * FROM "human";
id  firstName  lastName  socialSecurityNumber  email                   dateOfBirth  hasPet  numberOfCars
--  ---------  --------  --------------------  ----------------------  -----------  ------  ------------
1 John       Doe       123-45-6789 johndoe1990@gmail.com   1990-03-14   0       0
2 Anne       Ali       123-45-6790 alianne@gmail.com       1995-12-21   0       1
3 Gifty      Doe       123-45-6791 giftydoe@gmail.com      1995-01-11   1       0
4 Idris      Johnson   123-45-6792 johnidrisson@gmail.com  1992-06-30   0       2
sqlite>
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We also have the box mode

sqlite> .mode box
sqlite> SELECT * from "human";
┌────┬───────────┬──────────┬──────────────────────┬────────────────────────┬─────────────┬────────┬──────────────┐
│ id │ firstName │ lastName │ socialSecurityNumber │         email          │ dateOfBirth │ hasPet │ numberOfCars │
├────┼───────────┼──────────┼──────────────────────┼────────────────────────┼─────────────┼────────┼──────────────┤
│ 1  │ John      │ Doe      │ 123-45-6789          │ johndoe1990@gmail.com  │ 1990-03-14  │ 0      │ 0            │
│ 2  │ Anne      │ Ali      │ 123-45-6790          │ alianne@gmail.com      │ 1995-12-21  │ 0      │ 1            │
│ 3  │ Gifty     │ Doe      │ 123-45-6791          │ giftydoe@gmail.com     │ 1995-01-11  │ 1      │ 0            │
│ 4  │ Idris     │ Johnson  │ 123-45-6792          │ johnidrisson@gmail.com │ 1992-06-30  │ 0      │ 2            │
└────┴───────────┴──────────┴──────────────────────┴────────────────────────┴─────────────┴────────┴──────────────┘
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With this we have .exit to exit the SQLite runtime-environment (on the cli).

FILTERS

The idea about filters here, is to not unnecessarily select all the roles that we. We want to be able to select based on conditions and some particular amount at a time.

In the SELECT section, we know how to select only the fields we by passing the column's name.

We will need more rows here. You can download or access more data for insert. You can copy the content and paste it into any of the SQLite clients.

When the more data SQL file is download, we can insert its content by running this commend on SQLite

sqlite> .read more-data.sql
sqlite>
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Put more-data.sql in the same folder as app.sqlite or pass the path to more-data.sql

WHERE CLAUSE

The WHERE clause can be used to filter (conditional selection). This takes on the same syntax as SELECT with WHERE.

SELECT <FIELDS TO SELECT> FROM <TABLE NAME> WHERE <CONDITION FOR THE SELECTION>;
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  • Let's find humans that have pets. This means that we are interested in humans with the hasPet column to be 1. To do this we use =. 
   SELECT * FROM "human" WHERE "hasPet" = 1;
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  • So the = means is or equal-to. Unlike Javascript, =, single equal-to operator is used for assignment, whilst == or === is for equality check.
  • In javascript-part-four, we also discussed these operators
  • Is not equal to !=, so we can have <, >, <=, >=
  • Try selecting humans that have at least 2 cars
  • We have && as AND in Javascript, in SQL, it is AND. Same as || which is OR. With these we can have compound conditions.
  • Let's find humans that have a pet and at least two cars. 
   SELECT * FROM "human" WHERE "hasPet" = 1  AND "numberOfCars" >= 2;
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  • There is BETWEEN is used to find rows in ranges, "<COLUMN NAME> BETWEEN <START VALUE> AND <END VALUE>. Let's find humans whose IDs are between ranges of 3 and 10. 
   SELECT * FROM "human" WHERE "id" BETWEEN 3 AND 10;
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  • We can find humans who don't have pets but have between 2 to 4 cars. 
   SELECT * FROM "human" WHERE  "hasPet" = 0 AND ("numberOfCars" BETWEEN 2 AND 4);
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  • When "things" are getting complicated, wrap "things" in brackets and you will be fine.
  • We can find the rows of human whose IDs are in the array, [2,5,8,9] by using the IN operator. For this, we do, "<COLUMN NAME> IN (value1, value2, ..., valueN). 
   SELECT * FROM "human" WHERE "id" IN (1,2,5,8,9);
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  • We can also have a group of conditions and then negate them by using the NOT operator. 
   -- negate IN
   SELECT * FROM "human" WHERE "id" NOT IN (1,2,5,8,9);

   -- negate BETWEEN
   SELECT * FROM "human" WHERE "numberOfCars" NOT BETWEEN 1 AND 3;

   --negate compound conditions
   SELECT * FROM "human" WHERE NOT ("hasPet" = 0 AND ("numberOfCars" BETWEEN 2 AND 4));
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ORDER BY

By default, the rows are returned in a ascending order of ID. The rows are return in the order of the first created record to the latest. From the lowest to to the highest This is done by ORDER BY <COLUMN NAME> [DESC|ASC].

  • Let's see the default order, SELECT * FROM "human" WHERE "id" IN (1,2,5,8,9); Check the order order of the IDs 
   sqlite> SELECT * FROM "human" WHERE "id" IN (1,2,5,8,9);
   ┌────┬───────────┬──────────┬──────────────────────┬──────────────────────────┬─────────────┬────────┬──────────────┐
   │ id │ firstName │ lastName │ socialSecurityNumber │          email           │ dateOfBirth │ hasPet │ numberOfCars │
   ├────┼───────────┼──────────┼──────────────────────┼──────────────────────────┼─────────────┼────────┼──────────────┤
   │ 1  │ John      │ Doe      │ 123-45-6789          │ johndoe1990@gmail.com    │ 1990-03-14  │ 0      │ 0            │
   │ 2  │ Anne      │ Ali      │ 123-45-6790          │ alianne@gmail.com        │ 1995-12-21  │ 0      │ 1            │
   │ 5  │ Elarais   │ Kaelon   │ 123-45-6797          │ elarais.kaelon@gmail.com │ 1991-07-22  │ 1      │ 1            │
   │ 8  │ Peridot   │ Valor    │ 123-45-6800          │ peridot.valor@gmail.com  │ 1975-03-10  │ 1      │ 3            │
   │ 9  │ Aelis     │ Caspian  │ 123-45-6801          │ aelis.caspian@gmail.com  │ 1996-12-28  │ 0      │ 1            │
   └────┴───────────┴──────────┴──────────────────────┴──────────────────────────┴─────────────┴────────┴──────────────┘
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  • We can switch the order to DESC by passing, ORDER BY "id" DESC. SELECT * FROM "human" WHERE "id" IN (1,2,5,8,9) ORDER BY "id" DESC; 
   sqlite> SELECT * FROM "human" WHERE "id" IN (1,2,5,8,9) ORDER BY "id" DESC;
   ┌────┬───────────┬──────────┬──────────────────────┬──────────────────────────┬─────────────┬────────┬──────────────┐
   │ id │ firstName │ lastName │ socialSecurityNumber │          email           │ dateOfBirth │ hasPet │ numberOfCars │
   ├────┼───────────┼──────────┼──────────────────────┼──────────────────────────┼─────────────┼────────┼──────────────┤
   │ 9 │ Aelis     │ Caspian  │ 123-45-6801 │ aelis.caspian@gmail.com  │ 1996-12-28 │ 0 │ 1 │
   │ 8 │ Peridot   │ Valor    │ 123-45-6800 │ peridot.valor@gmail.com  │ 1975-03-10 │ 1 │ 3 │
   │ 5 │ Elarais   │ Kaelon   │ 123-45-6797 │ elarais.kaelon@gmail.com │ 1991-07-22 │ 1 │ 1 │
   │ 2 │ Anne      │ Ali      │ 123-45-6790 │ alianne@gmail.com        │ 1995-12-21 │ 0 │ 1 │
   │ 1 │ John      │ Doe      │ 123-45-6789 │ johndoe1990@gmail.com    │ 1990-03-14 │ 0 │ 0 │
   └────┴───────────┴──────────┴──────────────────────┴──────────────────────────┴─────────────┴────────┴──────────────┘
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FUNCTIONS

SQLite (SQL) supports functions for computing sum, SUM, count, COUNT, average, AVG, to find maximum, MAX, and minimum, MIN.

  • Let's sum the number of cars humans with pet have. 
   SELECT SUM("numberOfCars") FROM "human" WHERE "hasPet" = 1;
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  • The response to this is a little different from what we have seen so far 
   sqlite> SELECT SUM("numberOfCars") FROM "human" WHERE "hasPet" = 1;
   ┌─────────────────────┐
   │ SUM("numberOfCars") │
   ├─────────────────────┤
   │ 15                  │
   └─────────────────────┘
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  • Does SUM on non-numeric fields?
  • Let's count the number of humans with a pet. SELECT * FROM "human" WHERE "hasPet" = 1; returns rows of humans with pet. 
   sqlite> SELECT COUNT(*) FROM "human" WHERE "hasPet" = 1;
   ┌──────────┐
   │ COUNT(*) │
   ├──────────┤
   │ 14       │
   └──────────┘
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  • COUNT("id") will return the same response as COUNT(*) since it is the number of rows returned that countered.
  • We can find the average, AVG, in the same way as we did for SUM 
   sqlite> SELECT AVG("numberOfCars") FROM "human" WHERE "hasPet" = 1;
   ┌─────────────────────┐
   │ AVG("numberOfCars") │
   ├─────────────────────┤
   │ 1.07142857142857    │
   └─────────────────────┘
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  • MIN and MAX basically returns the minimum and maximum.
  • The default ordering is in ASC using the row's id. 
   sqlite> SELECT * FROM "human" WHERE "hasPet" = 1;
   ┌────┬───────────┬──────────┬──────────────────────┬──────────────────────────┬─────────────┬────────┬──────────────┐
   │ id │ firstName │ lastName │ socialSecurityNumber │          email           │ dateOfBirth │ hasPet │ numberOfCars │
   ├────┼───────────┼──────────┼──────────────────────┼──────────────────────────┼─────────────┼────────┼──────────────┤
   │ 3  │ Gifty     │ Doe      │ 123-45-6791          │ giftydoe@gmail.com       │ 1995-01-11  │ 1      │ 0            │
   │ 5  │ Elarais   │ Kaelon   │ 123-45-6797          │ elarais.kaelon@gmail.com │ 1991-07-22  │ 1      │ 1            │
   │ 7  │ Indigo    │ Rylanx   │ 123-45-6799          │ indigo.rylanx@gmail.com  │ 2001-09-01  │ 1      │ 0            │
   │ 8  │ Peridot   │ Valor    │ 123-45-6800          │ peridot.valor@gmail.com  │ 1975-03-10  │ 1      │ 3            │
   │ 10 │ Nyxus     │ Joveus   │ 123-45-6802          │ nyxus.joveus@gmail.com   │ 1984-06-03  │ 1      │ 2            │
   │ 12 │ Daxus     │ Onyx     │ 123-45-6804          │ daxus.onyx@gmail.com     │ 1970-02-20  │ 1      │ 1            │
   │ 14 │ Quillon   │ Lior     │ 123-45-6806          │ quillon.lior@gmail.com   │ 1997-04-25  │ 1      │ 1            │
   │ 15 │ Soren     │ Wren     │ 123-45-6807          │ soren.wren@gmail.com     │ 2003-01-07  │ 1      │ 0            │
   │ 17 │ Faelan    │ Zenith   │ 123-45-6809          │ faelan.zenith@gmail.com  │ 1986-05-30  │ 1      │ 1            │
   │ 19 │ Lumina    │ Saga     │ 123-45-6811          │ lumina.saga@gmail.com    │ 1972-03-29  │ 1      │ 2            │
   │ 21 │ Eira      │ Myrddin  │ 123-45-6813          │ eira.myrddin@gmail.com   │ 1998-05-19  │ 1      │ 1            │
   │ 23 │ Kestrel   │ Garnet   │ 123-45-6815          │ kestrel.garnet@gmail.com │ 2000-08-23  │ 1      │ 0            │
   │ 25 │ Solara    │ Roux     │ 123-45-6817          │ solara.roux@gmail.com    │ 1990-09-11  │ 1      │ 1            │
   │ 27 │ Aether    │ Phaedra  │ 123-45-6819          │ aether.phaedra@gmail.com │ 1995-01-05  │ 1      │ 2            │
   └────┴───────────┴──────────┴──────────────────────┴──────────────────────────┴─────────────┴────────┴──────────────┘
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  • If we want to find the minimum or maximum, we'd have to sort the rows. 
   sqlite> SELECT * FROM "human" WHERE "hasPet" = 1 ORDER BY "numberOfCars" DESC;
   ┌────┬───────────┬──────────┬──────────────────────┬──────────────────────────┬─────────────┬────────┬──────────────┐
   │ id │ firstName │ lastName │ socialSecurityNumber │          email           │ dateOfBirth │ hasPet │ numberOfCars │
   ├────┼───────────┼──────────┼──────────────────────┼──────────────────────────┼─────────────┼────────┼──────────────┤
   │ 8  │ Peridot   │ Valor    │ 123-45-6800          │ peridot.valor@gmail.com  │ 1975-03-10  │ 1      │ 3            │
   │ 10 │ Nyxus     │ Joveus   │ 123-45-6802          │ nyxus.joveus@gmail.com   │ 1984-06-03  │ 1      │ 2            │
   │ 19 │ Lumina    │ Saga     │ 123-45-6811          │ lumina.saga@gmail.com    │ 1972-03-29  │ 1      │ 2            │
   │ 27 │ Aether    │ Phaedra  │ 123-45-6819          │ aether.phaedra@gmail.com │ 1995-01-05  │ 1      │ 2            │
   │ 5  │ Elarais   │ Kaelon   │ 123-45-6797          │ elarais.kaelon@gmail.com │ 1991-07-22  │ 1      │ 1            │
   │ 12 │ Daxus     │ Onyx     │ 123-45-6804          │ daxus.onyx@gmail.com     │ 1970-02-20  │ 1      │ 1            │
   │ 14 │ Quillon   │ Lior     │ 123-45-6806          │ quillon.lior@gmail.com   │ 1997-04-25  │ 1      │ 1            │
   │ 17 │ Faelan    │ Zenith   │ 123-45-6809          │ faelan.zenith@gmail.com  │ 1986-05-30  │ 1      │ 1            │
   │ 21 │ Eira      │ Myrddin  │ 123-45-6813          │ eira.myrddin@gmail.com   │ 1998-05-19  │ 1      │ 1            │
   │ 25 │ Solara    │ Roux     │ 123-45-6817          │ solara.roux@gmail.com    │ 1990-09-11  │ 1      │ 1            │
   │ 3  │ Gifty     │ Doe      │ 123-45-6791          │ giftydoe@gmail.com       │ 1995-01-11  │ 1      │ 0            │
   │ 7  │ Indigo    │ Rylanx   │ 123-45-6799          │ indigo.rylanx@gmail.com  │ 2001-09-01  │ 1      │ 0            │
   │ 15 │ Soren     │ Wren     │ 123-45-6807          │ soren.wren@gmail.com     │ 2003-01-07  │ 1      │ 0            │
   │ 23 │ Kestrel   │ Garnet   │ 123-45-6815          │ kestrel.garnet@gmail.com │ 2000-08-23  │ 1      │ 0            │
   └────┴───────────┴──────────┴──────────────────────┴──────────────────────────┴─────────────┴────────┴──────────────┘
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  • By eye inspection or comparing the order of "numberOfCars" column, record with ID, 8, has highest number of cars and 23 has the lowest.
  • For MIN and MAX 
   sqlite> SELECT MIN("numberOfCars") FROM "human" WHERE "hasPet" = 1;
   ┌─────────────────────┐
   │ MIN("numberOfCars") │
   ├─────────────────────┤
   │ 0                   │
   └─────────────────────┘
   sqlite> SELECT MAX("numberOfCars") FROM "human" WHERE "hasPet" = 1;
   ┌─────────────────────┐
   │ MAX("numberOfCars") │
   ├─────────────────────┤
   │ 3                   │
   └─────────────────────┘
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  • How do we get the maximum number of cars among all the records?

UPDATE

The general syntax for an update looks like

UPDATE <TABLE NAME> SET <COLUMN 1> = <VALUE 1>, <COLUMN 2> = <VALUE 2>,..., <COLUMN N> = <VALUE N> WHERE <CONDITIONS>;
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The WHERE clause is optional.

There are two siblings, John and Gifty Doe. Gifty has a pet but John doesn't. John must have something. Let's updates John's row to increment the number of cars he has to 1. John's ID is 1. You can do this for any user.

UPDATE "human" SET "numberOfCars" = 1 WHERE "id" = 1;
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When human with ID 1 is selected, the numberOfCars column would have been updated to 1.

Try updating the email of human with email, giftydoe@gmail.com to giftydoe1995@gmail.com.

What do you think will happen when no WHERE clause is passed?

= is used as assignment operator here.

DELETE

The general syntax of DELETE is similar that of UPDATE.

DELETE FROM <TABLE NAME> WHERE <CONDITIONS>;
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The rows which match the condition are deleted. When there are no conditions or WHERE clauses, this action will affect the entire rows. As such use with caution.

  • SELECT humans with no pet and no cars.
  • How many are they? Use the COUNT function.
  • Let's DELETE these records. 
   DELETE FROM "human" WHERE "numberOfCars" = 0 AND "hasPet" = 0;
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  • Are there any records with no cars and no pet? Use the COUNT function.

SUMMARY

  • We can delete a table with DROP <TABLE NAME>;
  • We can insert with INSERT INTO <TABLE NAME> (...cols) VALUES (...vals);
  • Using the SELECT and WHERE, we can list records that meets a certain criteria
  • We can use SQL functions to reduce the number data manipulation we have to execute
  • We can update a record by, UPDATE <TABLE NAME> SET <col> = <val> WHERE <CONDITION>
  • We can delete a record by, DELETE FROM <TABLE NAME> WHERE <CONDITION>
  • When we use UPDATE and DELETE, where no WHERE clause is passed, these action will affect all the records

Top comments (1)

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leob profile image
leob • • Edited

Thorough overview, well done!