Detailed explanation of how to write the less than sign in MyBatis

Detailed explanation of how to write the less than sign in MyBatis

MyBatis is an excellent persistence layer framework that is widely used in Java development. In the process of using MyBatis for database operations, we often use the less than sign (

1. A simple example of using the less than sign

First, let’s look at a simple SQL query statement:

SELECT * FROM user WHERE age < 30;

In MyBatis, you can use parameterType and #{} placeholders are used to write the less than sign in the above SQL statement. The following is a simple MyBatis XML configuration file example:

<select id="selectUserByAge" parameterType="int" resultType="User">
    SELECT * FROM user WHERE age < #{age}
</select>

In the above example, #{age} is the placeholder, and MyBatis will replace age The value is replaced into the SQL statement.

2. Use the less than or equal sign and the greater than sign

In addition to the less than or equal sign, you can also use the less than or equal sign (<=) and the greater than sign (>) to perform conditional queries . The following is an example of using the less than or equal sign and the greater than sign at the same time:

<select id="selectUserByAgeRange" parameterType="Map" resultType="User">
    SELECT * FROM user WHERE age > #{minAge} AND age <= #{maxAge}
</select>

In the above example, a Map object is used as the parameter type, and the age range is implemented by passing in the two parameters minAge and maxAge. Inquire.

3. Use dynamic SQL to implement multi-condition query

Sometimes, we need to dynamically splice SQL statements based on different conditions. MyBatis provides <if># Tags such as ## and are used to implement dynamic SQL. The following is an example of using dynamic SQL to implement a less than sign query:

<select id="selectUserByCondition" parameterType="Map" resultType="User">
    SELECT * FROM user
    <where>
        <if test="minAge != null">
            AND age > #{minAge}
        </if>
        <if test="maxAge != null">
            AND age <= #{maxAge}
        </if>
    </where>
</select>

In the above example, the SQL statement is dynamically spliced ​​according to the conditions passed in. If minAge is passed in, the less than sign condition is added. If If maxAge is passed in, a less than or equal sign condition is added.

Through the above examples, we learned how to use the less than sign to perform conditional queries in MyBatis, and learned to use dynamic SQL to implement multi-condition queries. I hope this article can help you learn and use MyBatis.

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