LEFT(str,len)
返回字符串str的最左面len個字符。
SELECT LEFT('123456789',5)
eg:
#查詢"李"姓老師的數量
SELECT COUNT(*) AS 李姓老師的數量 FROM teacher WHERE Tname LIKE '李%';
select count(Tname) 李姓老師的數量 from Teacher where left(Tname,1) = '李';
select count(Tname) 李姓老師的數量 from Teacher where SUBSTRING(Tname ,1, 1) = '李';