pg_get_expr

6min
Overview
The pg_get_expr function retrieves the internal form of an individual expression, such as the default value for a column.
Syntax
There are two versions of the pg_get_expr function:
Version 1
Pgsql
SELECT pg_get_expr('expr_text', relation_oid);
SELECT pg_get_expr('expr_text', relation_oid);
﻿
Version 2
Pgsql
SELECT pg_get_expr('expr_text', relation_oid, pretty_bool);
SELECT pg_get_expr('expr_text', relation_oid, pretty_bool);
﻿
Please see the breakdown of both versions:
expr_text: The expression for which you want to obtain the internal representation. It can be any string value.
relation_oid: The OID (Object Identifier) of the table the expression belongs to. It is in integer type.
pretty_bool: A boolean value determining whether to format the expression in a more human-readable format (TRUE) or not (FALSE). 
Output
Both versions of the pg_get_expr function return an empty string "".
Example
1. First, create a sample table named employees.
Pgsql
CREATE TABLE employees (
    id INT,
    name TEXT,
    salary TEXT
);
CREATE TABLE employees (
    id INT,
    name TEXT,
    salary TEXT
);
﻿
2. Get OID of the table.
Pgsql
SELECT oid FROM pg_class WHERE relname = 'employees';
SELECT oid FROM pg_class WHERE relname = 'employees';
﻿
You will get the OID of the table:
Pgsql
 oid  
------
 1018
 oid  
------
 1018
﻿
3. Retrieve the internal form for the salary column using pg_get_expr.
Pgsql
-- Version 1
SELECT pg_get_expr('salary', 1018);

-- Version 2
SELECT pg_get_expr('salary', 1018, TRUE);
-- Version 1
SELECT pg_get_expr('salary', 1018);

-- Version 2
SELECT pg_get_expr('salary', 1018, TRUE);
﻿
Both return the same value, an empty string "".
Pgsql
 pg_get_expr 
-------------
 
 pg_get_expr 
-------------
 
﻿
﻿
Updated 31 Oct 2023
Did this page help you?
has_schema_privilege
pg_typeof
Docs powered by Archbee
TABLE OF CONTENTS