MySQL開發-判斷一個字串裡面包含幾個其他的字元,逐個獲取以分隔符間隔的字串
一、獲取一個字串中包含幾個指定的匹配字串
在儲存過程中要對一個字元中進行分割,獲取裡面以','分隔的各個字串,如:
'0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1'
要獲取該字串中有幾個',' ,寫法如下:
select
length('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1')-
length(replace('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',''));
解析:
先取得字串的總長度
length('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1')
使用replace把','替換成''後,再獲取替換後的字串的長度
length(replace('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',''));
','的數量=原始長度-替換後的長度
二、逐個獲取以分隔符間隔開的每個字串
如要獲取上面的字串以','分隔開的每個字串
'0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1'
先按上面的方法獲取有多少個字串 N: ','的數量+1
手工逐個獲取如下:
第一個:0102_001956B_1
select replace(substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',1), concat(substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',0),','),'');
第N個:0102_001952E_1
select replace(substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',N
原理:
使用substring('字串', '分隔符', n) 可以擷取字串中以分隔符分開的前n個串(帶分隔符)
如取前2個串:
select substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',2);
再取前1個串:
select substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',1);
這樣,要獲取第2個串,就在前2個串的基礎上把 “前1個串+ ',' ” 用 ''替換掉,則剩餘的便是第2個串
select replace(substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',2), concat(substring_index('0102_001956B_1,0102_001955A_1,0102_001954C_1,0102_001953D_1,0102_001952E_1',',',1),','),'');
單個的分隔串取出來的,要逐個獲取則使用迴圈從最低位開始逐一獲取即可:虛擬碼如下
獲取有多少個字串 N: '分隔符'的數量+1 ;
設定迴圈開始位 i=0 (0用於獲取第1個串);
while i<N do
select replace(substring_index(str,',',i+1),concat(substring_index(str,',',i),','),'') ; (獲取第i+1個串值)
set i=i+1;
end while;