How Can I Effectively Use Script Variables in psql?

Use script variables efficiently in psql

PostgreSQL uses the set command to define variables. For example:

<code class="language-sql">\set myvariable value</code>

Once defined, variables can be replaced seamlessly. One way is to replace it directly, for example:

<code class="language-sql">SELECT * FROM :myvariable.table1;</code>

In addition, variables can also be used in conditional string queries. For example:

<code class="language-sql">SELECT * FROM table1 WHERE column1 = :'myvariable';</code>

But in psql versions before 9.1, if you use a variable as a value in a conditional string query, you need to include quotes in the variable definition:

<code class="language-sql">\set myvariable 'value'</code>

Additionally, to generate quoted and unquoted strings from existing variables, you can use the following trick:

<code class="language-sql">\set quoted_myvariable '\'' :myvariable '\''</code>

This allows the flexibility to use variables in various string contexts, for example:

<code class="language-sql">INSERT INTO :myvariable.table1 SELECT * FROM table2 WHERE column1 = :quoted_myvariable;</code>

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