How Can I Cast Data Types in PostgreSQL SELECT Statements?

Convert data types in PostgreSQL SELECT statement

PostgreSQL 8 and above allows data type conversion in SELECT statements. For example, to convert a varchar column to type int, you can use one of the following syntaxes:

<code class="language-sql">cast(varchar_col AS int)  -- SQL 标准语法</code>

or

<code class="language-sql">varchar_col::int          -- PostgreSQL 简写语法</code>

The two syntaxes can usually be used interchangeably unless specific syntax restrictions are encountered.

Also, consider the following forms:

<code class="language-sql">int4(varchar_col)         -- 对某些类型名称有效
int '123'                 -- 无类型，带引号的字符串字面量</code>

It should be noted that the last form does not support array types. For array types, you need to use '{1,2,3}'::int[] or cast('{1,2,3}' AS int[]).

When converting a string to an int, the string should only contain optional symbols (/-) followed by digits. Leading and trailing spaces are ignored. For more details, please refer to the PostgreSQL documentation linked below.

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