是否可以使用“WHERE"?子句选择SQL语句中的所有记录? [英] Is it possible to use "WHERE" clause to select all records in SQL Statement?

问题描述

晚上好，我很好奇是否可以在可以显示所有记录的 SQL 语句中创建一个 WHERE 子句?

下面是一些解释:

<块引用>

随机 SQL 语句(Java)-(JSP 示例)，正常情况

String SqlStatement = "SELECT * FROM table_example WHERE First_Col = '<%=passVar%>'";db.query(SqlStatement);//........//........

如果passVar 是'ALL'，并且当passVar = All 时我们需要提示所有记录怎么办?我知道我可以使用 if-else 并检查 passVar 是否为ALL"，然后查询 without-WHERE 语句 以使其工作..

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**without-WHERE 语句(Java)-(JSP 示例)**

if(<%=passVar%> == "ALL") {SqlStatement = "SELECT * FROM table_example";} 别的 {SqlStatement = "SELECT * FROM table_example WHERE First_Col = '<%=passVar%>'";}

但是我可以只编写一个 SQL 语句来使所有记录都提示吗?类似于以下内容:

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(Java)-(JSP 示例)

String ShowAll = "";if(<%=passVar%> == "ALL") {显示全部 = *;} 别的 {ShowAll = <%=passVar%>;}SqlStatement = "SELECT * FROM table_example WHERE First_Col = ShowAll ";

解决方案

这也有效:

WHERE 列名 LIKE '%'

NULL 值除外.

Good Evening, I am curious if it is possible to make a WHERE-clause in a SQL statement which can show all records?

Below some explanation:

Random SQL Statement (Java)-(JSP example), Normal Situation

String SqlStatement = "SELECT * FROM table_example WHERE First_Col = '<%=passVar%>' ";
db.query(SqlStatement );
//........
//........

What if the passVar is 'ALL', and we need to prompt all the records out when passVar = All? I know I can do it with if-else and check if the passVar is "ALL" then query the without-WHERE statement to make it work..

**without-WHERE statement (Java)-(JSP example)**

if(<%=passVar%> == "ALL") {
   SqlStatement = "SELECT * FROM table_example";
} else {

   SqlStatement = "SELECT * FROM table_example WHERE First_Col = '<%=passVar%>' ";
}

but can I just code one SQL statement to make all the records prompt? Something like below:

(Java)-(JSP example)

String ShowAll = "";
if(<%=passVar%> == "ALL") {
    ShowAll = *;

} else {
    ShowAll = <%=passVar%>;
}
SqlStatement = "SELECT * FROM table_example WHERE First_Col = ShowAll ";

解决方案

This also works:

WHERE columnname LIKE '%'

Except for NULL values.

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