在特定单词位置之前/之后替换字符串中的单词？ （SQL语句）

Question

说我有以下示例字符串：

SELECT a, b, c FROM table1 ORDER BY c

我如何（通过字符串操作）将SELECT a, b, c更改为SELECT COUNT(a)并删除ORDER BY子句？

我需要在我的代码中生成一个生成的查询并对其进行修改，以便我可以运行查询的COUNT()版本，并显示一个标签，其中包含标记为打印总数的记录数。

修改

假设我有一个更复杂的查询，我正在执行联合。为了获得与上面提到的相同的功能，我需要做什么？我只是将我的第一个SELECT条款更改为COUNT(*)或......？

SELECT a.memno, 
a.name, 
a.addr1, 
a.addr2, 
a.city, 
a.state, 
a.zip, 
a.sex, 
a.lname, 
a.ssan, 
b.addr1 as old_addr1, 
b.addr2 as old_addr2, 
b.city as old_city, 
b.state as old_state, 
b.zip as old_zip, 
b.timec 

FROM library1.table1 a, library1.table2 b 
WHERE a.memno = b.memno and 
b.groupid = 'P2' and 
b.type = 'B' and 
b.datec = 20131206 AND 
(a.addr1 <> b.addr1 or a.addr2 <> b.addr2 or a.city <> b.city or a. state <> b.state or a.zip <> b.zip) 
UNION 
SELECT 
a.memno, 
a.name, 
a.addr1, 
a.addr2, 
a.city, 
a.state, 
a.zip, 
a.sex, 
a.lname, 
a.ssan, 
b.addr1 as old_addr1, 
b.addr2 as old_addr2, 
b.city as old_city, 
b.state as old_state, 
b.zip as old_zip, 
b.timec 

FROM library2.table1 a, library2.table2 b 
WHERE a.memno = b.memno and 
b.groupid = 'N2' and 
b.type = 'B' and 
b.datec = 20131206 AND 
(a.addr1 <> b.addr1 or a.addr2 <> b.addr2 or a.city <> b.city or a. state <> b.state or a.zip <> b.zip) ORDER BY timec desc

Answer 1

如果字符串真的一致，一种方法是：

var input = "SELECT a, b, c FROM table1 ORDER BY c";
var output = input.Replace(
    input.Substring(0, input.IndexOf("FROM") - 1),
    "SELECT COUNT(*)");

var orderByIndex = output.IndexOf("ORDER BY");
var output = output.Replace(
    output.Substring(orderByIndex, output.Length - orderByIndex),
    "");

我知道我在使用SELECT COUNT(*)，但这是为了保持算法简单。如果您通过其他方式可以随时获得关键字段，请将其插入，但我会说如果您必须将其从字符串中删除，则解析的复杂性不值得分解。

Answer 2

一种可能的解决方案是将整个查询放入子查询中进行计数（假设您不关心ORDER子句）：

SELECT COUNT(1) FROM (
    SELECT a, b, c FROM table1 ORDER BY c
)