P34 字符串类型的函数讲解

2.字符串函数

#2.字符串函数
SELECT ASCII('abc'),CHAR_LENGTH('hello'),CHAR_LENGTH('我们'),
LENGTH('hello'),LENGTH('我们')
FROM DUAL;# xxx worked for yyy
SELECT CONCAT(emp.last_name,'worked for',mgr.last_name)
FROM employees emp JOIN employees mgr
WHERE emp.manager_id = mgr.employee_id;SELECT CONCAT_WS('-','hello','world','hello','beijing')
FROM DUAL;
#字符串的索引从1开始的！
SELECT INSERT('helloworld',2,3,'aaaaa'),REPLACE('hello','ll','mmm')
FROM DUAL;SELECT UPPER('hello'),LOWER('HeLlo')
FROM DUAL;SELECT LEFT('hello',2),RIGHT('hello',3),RIGHT('hello',13)
FROM DUAL;#LPAD:实现右对齐效果
#RPAD:实现左对齐效果
SELECT employee_id,last_name,LPAD(salary,10,' ')
FROM employees;SELECT LENGTH(TRIM('   h el   lo  ')),
TRIM('o' FROM 'ooheollo')
FROM DUAL; SELECT REPEAT('hello',4),LENGTH(SPACE(5)),STRCMP('abc','abd')
FROM DUAL;SELECT SUBSTR('hello',2,2),LOCATE('ll','hello')
FROM DUAL;SELECT ELT(2,'a','b','c','d'),FIELD('mm','gg','jj','mm','dd','mm'),
FIND_IN_SET('mm','gg,mm,jj,dd,mm,gg')
FROM DUAL;SELECT employee_id,NULLIF(LENGTH(first_name),LENGTH(last_name))"compare"
FROM employees;

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