PostgreSQL NULL

NULL 判断用 IS NULL / IS NOT NULL；COALESCE 取第一个非 NULL 值，NULLIF 两值相等时返回 NULL。

Intermediate

Key PointsPostgreSQL,NULL,COALESCE,NULLIF

讲解

NULL 判断用 IS NULL / IS NOT NULL；COALESCE 取第一个非 NULL 值，NULLIF 两值相等时返回 NULL。

SQL

SELECT name, COALESCE(salary, 0) AS sal FROM company;
SELECT NULLIF(0, 0);      -- 返回 NULL
SELECT * FROM company WHERE salary IS NULL;

NULL 判断用 IS NULL / IS NOT NULL；COALESCE 取第一个非 NULL 值，NULLIF 两值相等时返回 NULL。

SQL

SELECT name, COALESCE(salary, 0) AS sal FROM company;
SELECT NULLIF(0, 0);      -- 返回 NULL
SELECT * FROM company WHERE salary IS NULL;