今天在写SQL过滤条件时，有个URL判空逻辑，想当然的写成了如下格式:1select * from record where url != null 然而，明明有符合条件的数据， ... ... <看更多>

SQL Null check is performed using either IS NULL or IS NOT NULL to check whether a value in a field is NULL or not.When a field value is ... ... <看更多>

Learn how to use the SQL IS NULL Condition to test for a NULL value in SQL. This tutorial explains what a NULL value is and demonstrates how ... ... <看更多>