其中,第一个查询使用比较运算符判断空值,不会返回任何结果;第二个查询使用 IS NULL 判断空值,返回了正确的结果。 除了标准的IS [NOT] NULL之外,还有一些数据库扩展的运算符可以用于空值比较: -- MySQL SELECT employee_id, first_name, last_name, manager_id FROM employees WHERE manager_id <=> NULL; empl...
SQL>selectlpad('what is this',5),lpad('what is this',25),lpad('what is this',25,'-')fromdual;---用指定的字符串(what is this)从左补齐多少个字符(5个)字符串不够的用-补齐,what is this',5,'-' trim去空格的 replace替换 SQL>selectreplace('wwwjkdkdddww is ssseess','w','-') ...
It’s good for translating data back to the users or systems that access it. It’s also good for aggregate functions and grouping, so you can actually see what a NULL value is. ISNULL (SQL Server, MySQL) This function is the same as NVL: it allows you to use a different value if ...
SQL>select lpad('what is this',5),lpad('what is this',25),lpad('what is this',25,'-') from dual; ---用指定的字符串(what is this)从左补齐多少个字符(5个)字符串不够的用-补齐,what is this',5,'-' 1. trim去空格的 replace替换 SQL>select replace('wwwjkdkdddww is ssseess','w...
NVL函数:NVL函数用于将NULL值替换为指定的值。它接受两个参数,第一个参数是要检查的值,第二个参数是要替换的值。例如,NVL(column_name, 'N/A')将返回column_name的值,如果为NULL,则返回'N/A'。 IS NULL和IS NOT NULL运算符:这些运算符用于检查一个值是否为NULL或非NULL。可以在WHERE子句中使用它们来过滤...
ix Data Warehouse Service SQL Syntax 1 About GaussDB(DWS) SQL 1 About GaussDB(DWS) SQL What Is SQL? SQL is a standard computer language used to control the access to databases and manage data in databases. SQL provides different statements to enable you to: ● Query data. ● Insert, ...
select INITCAP('whaT is this') from dual;---首字母大写,其余小写 select TO_MULTI_BYTE('ABC abc中华') from dual;---半角变全角 select TO_SINGLE_BYTE('ABC abc中华') from dual;---全角变半角 select VSIZE('abc中华') from dual;---返回字节数 select INSTR('CORPORATE ...
|WhaT| WhaT is tHis | WhaT is tHis--- 作用:作为调整格式的输出,例: with x as ( select 'aa' chr from dual union all select 'bb' chr from dual) select level ,chr,lpad( ' ' ,( level - 1 )* 5 , '-' )||chr other from x connect by level <= 3 说明:若LPAD对空...
select INITCAP('whaT is this') from dual;---首字母大写,其余小写 select TO_MULTI_BYTE('ABC abc 中华') from dual;---半角变全角 select TO_SINGLE_BYTE('ABCabc中华') from dual;---全角变半角 select VSIZE('abc中华') from dual;---返回字节数 select INSTR('CORPORATE FLOOR','OR',3...
The functions in Oracle to handle NULL values are NVL and NVL2. NVL(expression1,expression2) TheNVL functionwill check expression1. If expression1 is not NULL, it is returned. If expression1 is NULL, then expression2 is returned. It’s like a simple IF statement. ...