SQL条件语句 [英] SQL conditional statement

问题描述

我正在尝试在ORACLE sql代码中创建条件语句
我在java中有一个带有2个参数的函数。
getchildren（child1，child2） ..此函数的参数用于创建查询语句

I'm trying to create a conditional statement in an ORACLE sql code I have a function in java that takes 2 parameters. getchildren(child1,child2)..this function's parameters are used to create a query statement

public ResultSet getchildren(String Child1, String child2) throws SQLException 
{

 stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,
 ResultSet.CONCUR_READ_ONLY);


     query ="select * from table1 

            if child1 is not null and child2 is null
            { where child1 = 1 }
            else if child2 is not null AND child1 is null
            {where child2 = 2}
            else
             {//some other where statment } 
            ";



    System.out.println("\nExecuting query: " + query);
    rset = stmt.executeQuery(query);

    return rset;


}

这显然是伪代码。
我需要帮助为 where 子句创建条件执行，以便在条件有效时执行每个where子句。我尝试过类似于我的东西，但没有运气。

This is obviously pseudocode. I need help creating a conditional execution for the where clauses so that each "where" clause is executed when its condition is valid. I've tried something similar to what I have up there but with no luck.

推荐答案

使用StringBuilder动态构建查询。

Use a StringBuilder to dynamically build your query.

StringBuilder queryBuilder = new StringBuilder();
queryBuilder.append("select * from table1 ");

if ( child1 != null && child2 == null) 
   queryBuilder.append(" where child1 = 1 ");
else if ( child2 != null && child1 == null)
   queryBuilder.append(" where child2 = 1 ");
else
   queryBuilder.append(" where bla ");

// Execute queryBuilder.toString();
rset = stmt.executeQuery(queryBuilder.toString());

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