After the parser generates a parse tree, the analyzer/analyser performs a semantic analysis on it and generates a query tree. The root of the query tree is represented by the Query structure defined in parsenodes.h, which contains essential metadata about the command type (SELECT, INSERT, or others) and various leaves. Each leaf in the query tree forms a list or a tree and holds specific data related to individual clauses.
In the generated query tree, the targetlist represents the columns that will be included in the query result. For the given example, the targetlist consists of two columns: 'id' and 'data'. In cases where the input query tree uses an asterisk symbol ('*'), the analyzer/analyser replaces it explicitly with all the columns.
The range table, another component of the query tree, contains information about the relations used in the query. For the provided query, the range table would hold details about the 'tbl_a' table, including its object identifier (OID) and name.
The join tree is responsible for storing the FROM clause and the WHERE clauses, capturing the relationships and conditions between tables.
Lastly, the sort clause is a list of SortGroupClause, which defines the sorting behavior specified in the ORDER BY clause.
Through its semantic analysis, the analyzer/analyser transforms the parse tree into a query tree, enabling further processing and execution of the SQL query.
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