如何在MySQL中处理复杂的条件where子句

Question

Based on a variety of optional user inputs, I need to modify the structure of the where clause in query (not just dynamic values, but dynamic structure).
Examples.. if they select a customerID, then don't use the branchID filter, but if they select an empID then use both empID and branchID filters. There are more criteria that are used as well, thats just an example.

I could build all the logic into the where clause using CASE statements, but I'm guessing that wouldn't be very well optimized? I know I could dynamically build the sql statement within a stored proc, and i could use prepared statements as well... but that seems sloppy? Is there another method I'm not thinking of?

Answer 1

The usual approach is dynamically building the query in the layer that handles the user input. In case you do not use a high level language in front of your database, this means resorting to a stored procedure indeed, and this might look a bit dirty indeed - I too find this language quite awkward.

A pure SQL solution does not have too much of an overhead, since constant-based conditions will be optimized away quite efficiently (user input is constant when the query starts).

Answer 2

I have typically done what you are doing using bind variables and a conditional query, like so:

SELECT ...
FROM table
WHERE ...(put your where clause elements common to both cases here)
AND ((? = 'value1'
       AND ...
       AND ...
    ) OR
    (? = 'value2'
       AND ...
       AND ...
    ))
GROUP BY ...
ORDER BY ...

? is the bind variable syntax for MySQL -- see Listing 23 here for a small example. In this case, bind vars 1 and 2 would actually be set to the same value.

You can also do the same sort of thing with a CASE statement.

Answer 3

mybatis dynamic sql may helps you。

<select id="findActiveBlogLike"
     resultType="Blog">
  SELECT * FROM BLOG WHERE state = ‘ACTIVE’
  <choose>
    <when test="title != null">
      AND title like #{title}
    </when>
    <when test="author != null and author.name != null">
      AND author_name like #{author.name}
    </when>
    <otherwise>
      AND featured = 1
    </otherwise>
  </choose>
</select>