Postgresql常用函数及使用方法大全(看一篇就够了)

-- 查看postgresql的版本(以下任一语句都可以实现)
select version();
show server_version;

-- 将文本'123'转为int8类型
SELECT
    '123' :: int8 num;
-- 将文本类型字段t1转为int8类型
SELECT
    t1 :: int8 
    from temp;

-- 将文本'123'转为int8类型
SELECT
    int8'123' num;

-- 将文本'123'转为int8类型
SELECT
    cast('123' as int4) num;
-- 将文本字段t1转为int类型
SELECT CAST( t1 AS INT ) t1_c 
FROM
    TEMP;

-- 文本转整数
SELECT CAST
    ( '123' AS int4 );
-- 文本转浮点数字
SELECT CAST
    ( '123.34' AS DECIMAL );
SELECT CAST
    ( '123.34' AS NUMERIC );
-- 数字转文本
SELECT CAST
    ( 123 AS VARCHAR );--可变字符串
SELECT CAST
    ( - 123 AS CHAR ( 2 ) );-- 固定字符串，进行截断，将-123转为'-1'
SELECT CAST
    ( - 123 AS CHAR ( 6 ) );-- 固定字符串，进行空格填充，将-123转为'-123  '
SELECT CAST
    ( 124.94 AS TEXT );--可变字符串,将124.94转为'124.94'
SELECT
    to_char( 124.94, '999D9' );--将124.94转为'124.9',遵循四舍五入
SELECT
    to_char( 124.94, 'FM999.99' );--将124.94转为'124.94'
SELECT
    to_char( - 124.94, 'FM9999999.99' );--将-124.94转为'-124.94'
SELECT
    to_char( - 124.94, 'FM9999999.990' );--将-124.94转为'-124.940'
SELECT
    to_char( 124, '00000' );--左端用零补齐凑够5位，将124转为'00124'
SELECT
    to_char( 124, '99999' );--左端用空格补齐凑够5位，将124转为'  124'
SELECT
    to_char( - 124.945, 'FM999' );--只显示整数部分，遵循四舍五入
-- 时间戳(timestamp)转日期(date)
SELECT CAST
    ( now( ) AS DATE );--普通日期模式
-- 时间戳(timestamp)转文本
SELECT CAST
    ( now( ) AS TEXT );--不指定输出格式
SELECT
    to_char( now( ), 'yyyy-mm-dd' );--指定输出格式;
-- 文本转日期(date)
SELECT
    to_date( '2012-01-01', 'yyyy-mm-dd' );
-- 文本转时间戳(TIMESTAMP)
SELECT
    to_timestamp( '2012-01-01 12:02:01', 'yyyy-mm-dd HH24:MI:SS' );

WITH test_table AS (
	SELECT UNNEST( ARRAY [ '财务', '行政', '销售', '财务', '行政', '行政' ] ) AS depart,
		UNNEST ( ARRAY [ 'A', 'B', 'A', 'C', 'D', 'C' ] ) AS NAME,
		UNNEST ( ARRAY [ 200, 100, 50, 30, 200, 100 ] ) AS donate 
	) SELECT
	depart,
	NAME,
	GROUPING ( depart, NAME ),
	SUM ( donate ),
	COUNT ( donate ) 
FROM
	test_table 
GROUP BY
	ROLLUP ( depart, NAME );

-- 查看所有函数名，返回类型，及参数个数
SELECT
  pg_proc.proname AS "函数名称",
  pg_type.typname AS "返回值数据类型",
  pg_proc.pronargs AS "参数个数"
FROM
  pg_proc
JOIN pg_type ON (pg_proc.prorettype = pg_type.oid)
-- WHERE pronamespace = (SELECT pg_namespace.oid FROM pg_namespace WHERE nspname = '模式')