How Can I Effectively Use Script Variables in psql for Dynamic SQL Queries?

Effective use of psql script variables

PostgreSQL’s psql client allows the creation of customizable values ​​at runtime using script variables, enabling dynamic adjustment of SQL script parameters.

To create a variable in psql, use the set command, followed by the variable name and its assignment. For example, define a variable named "myvariable" and set its value to "value3":

<code>\set myvariable value3</code>

Use the ":variable_name" syntax to replace variables into SQL queries. For example, to select all rows from a table where a specific column matches the value stored in "myvariable", you can use the following query:

<code>SELECT * FROM table1 WHERE column1 = :myvariable;</code>

In psql 9.1 and later, variables can be expanded within quotes without any modification. But in earlier versions, if you planned to use a variable as a value in a conditional string query, you needed to include quotes in the variable, like this:

<code>\set myvariable 'value3'
SELECT * FROM table1 WHERE column1 = ':myvariable';</code>

If you need quoted and unquoted versions of a variable, you can create another quoted variable using the following syntax:

<code>\set quoted_myvariable '\'' :myvariable '\''</code>

Through these technologies, you can easily utilize script variables in psql to enhance the flexibility and reusability of SQL scripts.

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