SELECT Statement

The SELECT statement can be executed to retrieve data from a table or view. The result is stored in a result table, which is called a result set.

Serving as an overlaid filter for a database table, the SELECT statement filters required data from the table using SQL keywords.

Syntax

SELECT 
{ * | [column, ...] }
[ FROM from_item [, ...] ];

Parameter Description
SELECT list

Specifies the name of a column in the table to be queried. The value can be a part of the column name or all of the column names. The wildcard (*) is used to represent all column names.

Column names can be expressed in the following formats:

Manually input column names which are separated by commas (,)
Columns computed in the FROM clause
FROM clause

Specifies one or more source tables for the SELECT statement. The FROM clause involves multiple elements. The common elements are as follows:

table_name

Specifies the name of a table or view. The schema name can be added before the table name or view name, for example, schema_name.table_name. The table name is the most common element.

subquery

Performs a subquery in the FROM clause. A temporary table is created to save subquery results. For details, see Subqueries.

alias

Gives a temporary alias to a table to facilitate the reference by other queries. For details, see Aliases.

join_type

There are five types. For details, see JOIN.

Examples
Read all data from the customer_t1 table.

openGauss=# SELECT * FROM customer_t1;
c_customer_sk | c_customer_id | c_first_name | c_last_name | amount
---------------+---------------+--------------+-------------+--------
          3869 | hello         | Grace        |             |   1000
          3869 | hello         | Grace        |             |   1000
          3869 |               | Grace        |             |
          3869 | hello         |              |             |
          3869 | hello         |              |             |
               |               |              |             |
          6985 | maps          | Joes         |             |   2200
          9976 | world         | James        |             |   5000
          4421 | Admin         | Local        |             |   3000
(9 rows)

Read the c_customer_sk and c_customer_id columns from the customer_t1 table.

openGauss=# SELECT c_customer_sk,c_customer_id FROM customer_t1;
c_customer_sk | c_customer_id
---------------+---------------
          3869 | hello
          3869 | hello
          3869 |
          3869 | hello
          3869 | hello
               |
          6985 | maps
          9976 | world
          4421 | Admin
(9 rows)