某些其他数据库让它们在任何参数为 NULL 时返回 NULL,而不是在所有参数都为 NULL 时才返回 NULL。 1.2 nullif NULLIF(value1, value2) 当value1和value2相等时,NULLIF返回一个空值。 否则它返回value1。 1.3 COALESCE COALESCE(value [, ...]) COALESCE函数返回它的第一个非空参数的值。当且仅当所有参数都...
1、mysql中的ifnull()函数对应postgresql的coalece COALESCE('字段名称','期望值') 2、示例 select COALESCE(p.valid,0) ,p.valid &... 查看原文 mysql的COALESCE函数、NULLIF函数、IFNULL函数 一、COALESCE函数返回从左至右第一个非空表达式的值。COALESCE(expr1, expr2, ..., expr_n)selectcoalesce(null...
'index hit rate' AS name, (sum(idx_blks_hit)) / nullif(sum(idx_blks_hit + idx_blks_read),0) AS ratio FROM pg_statio_user_indexes UNION ALL SELECT 'table hit rate' AS name, sum(heap_blks_hit) / nullif(sum(heap_blks_hit) + sum(heap_blks_read),0) AS ratio FROM pg_statio_...
如果$1为空且first_name不为空，则将比较first_name = first_name（True）如果$1不为空且first_name...
如果$1为空且first_name不为空，则将比较first_name = first_name（True）如果$1不为空且first_name...
In this SQL tutorial, we have reviewed the SQL (structured query language) functions COALESCE(), ISNULL(), NULLIF() and how these work in SQL Server, Oracle and PostgreSQL. There are also other ways for checking NULL values such as the IS NULL clause and there are other complex functions...
PostgreSQL has a function name “COALESCE” [3]. The function takes n number of arguments and returns the first, not null arguments. You can test your expression against NULL using the function. Shell 1 COALESCE (NULL, 2 , 1); NULLIF There is another function called “NULLIF”[3], retur...
COALESCE– return the first non-null argument. You can use it to substituteNULLby a default value. NULLIF– returnNULLif the first argument equals the second one. CAST– convert from one data type into another e.g., from a string into an integer, from a string into a date. ...
CREATE OR REPLACE FUNCTION nvl(text, text) RETURNS text LANGUAGE sql AS $$ select coalesce(NULLIF($1,''), NULLIF($2,'')) $$; Let’s test the NVL wrapper function we created and see if it can handle NULL as well empty strings: postgres=> SELECT coalesce('', 'A') res; re...
COALESCE 238 9.17.3. NULLIF 239 9.17.4. GREATEST and LEAST 239 9.18. 数组函数和操作符 239 9.19. 范围函数和操作符 242 9.20. 聚合函数 244 9.21. 窗口函数 249 9.22. 子查询表达式 250 9.22.1. EXISTS 250 9.22.2. IN 251 9.22.3. NOT IN 251 9.22.4. ANY/ SOME 252 9.22.5. ALL 252 ...