How to Cast Data Types in PostgreSQL?

Detailed explanation of PostgreSQL data type conversion

When using a PostgreSQL database, you may need to convert the data type of a column to another type. For example, you might need to convert a varchar type column to an int type.

Type conversion method

In PostgreSQL, you can use the following methods for data type conversion:

<code class="language-sql">cast(<column_name> AS <new_data_type>)
cast(<column_name> AS INTEGER) -- 显式指定新类型</column_name></new_data_type></column_name></code>

For example, convert a varchar column named "my_column" to type int:

<code class="language-sql">SELECT CAST(my_column AS INTEGER) FROM my_table;</code>

Other syntax

• PostgreSQL shorthand syntax:

<code class="language-sql"><column_name>::<new_data_type></code>

For example:

<code class="language-sql">my_column::INTEGER</code>

• Int4(column_name):

Applies to certain type names. Example of int type:

<code class="language-sql">int4(my_column)</code>

• Int 'value':

Must be an untyped quoted string literal. For example:

<code class="language-sql">int '123'</code>

Notes

• The string must consist of a leading symbol (/-) followed by a number.
• Leading/trailing spaces will be ignored.
• The last item (int 'value') is not available for array types.

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