What are the dynamic SQL tags in mybatis?

mybatis dynamic SQL tags: 1. f3bf5eff46860b27119c8dd4e92f1e57 tag; 2. c88e008ca37f641f1d68866f53b5c0de, bb41c5e2afa2e51b56cbbc78bba5590f and 08840e2c213e7be6cb36177580c1b0f8 tags; 3. 800a174bf160103126f2a6097b3e44a4 tag; 4. f25103d1f946444d908430d39cff9ca4 and ace372f96ca3ec664acb3aaa2421b04c tags; 5. 94561e999a5eec0e6ba7d7040437c3f1 tag. Detailed introduction: 1. The f3bf5eff46860b27119c8dd4e92f1e57 tag is used to determine whether a certain SQL statement is included based on conditions. It is similar to the if statement in Java; 2. c88e008ca37f641f1d68866f53b5c0de, bb41c5e2afa2e51b56cbbc78bba5590f and 08840e2c213e7be6cb36177580c1b0f8 tags, etc. wait.

The operating system for this tutorial: Windows 10 system, DELL G3 computer.

MyBatis is an excellent persistence layer framework that supports customized SQL, stored procedures and advanced mapping. In MyBatis, dynamic SQL is a very powerful feature that allows developers to build flexible SQL queries based on different conditions. MyBatis provides a variety of dynamic SQL tags for dynamically generating SQL statements at runtime. The following are commonly used dynamic SQL tags in MyBatis:

1, f3bf5eff46860b27119c8dd4e92f1e57 Tag: f3bf5eff46860b27119c8dd4e92f1e57 The tag is used to determine whether a certain SQL statement is included based on conditions. It is similar to if statement in Java. For example:

<select id="findUsers" resultType="User">  
  SELECT * FROM user  
  WHERE 1=1  
  <if test="name != null">  
    AND name = #{name}  
  </if>  
  <if test="age != null">  
    AND age = #{age}  
  </if>  
</select>

2, c88e008ca37f641f1d68866f53b5c0de, bb41c5e2afa2e51b56cbbc78bba5590f and 08840e2c213e7be6cb36177580c1b0f8 Tags: These tags are used to implement a switch-case-default structure similar to Java. The c88e008ca37f641f1d68866f53b5c0de tag contains multiple bb41c5e2afa2e51b56cbbc78bba5590f and an 08840e2c213e7be6cb36177580c1b0f8 tag. When the attribute value of the c88e008ca37f641f1d68866f53b5c0de tag is true, the content in the corresponding bb41c5e2afa2e51b56cbbc78bba5590f tag is executed. If none of the bb41c5e2afa2e51b56cbbc78bba5590f tags have a property value of true, the contents of the 08840e2c213e7be6cb36177580c1b0f8 tag are executed. For example:

<select id="findUsers" resultType="User">  
  SELECT * FROM user  
  WHERE 1=1  
  <choose>  
    <when test="name != null">  
      AND name = #{name}  
    </when>  
    <when test="age != null">  
      AND age = #{age}  
    </when>  
    <otherwise>  
      AND is_active = 1  
    </otherwise>  
  </choose>  
</select>

3, 800a174bf160103126f2a6097b3e44a4 Tag: 800a174bf160103126f2a6097b3e44a4 tag is used to traverse a collection or array in a SQL statement and generate the corresponding SQL fragment. It is often used in scenarios such as IN queries or batch inserts. For example:

<select id="findUsersByIds" resultType="User">  
  SELECT * FROM user WHERE id IN   
  <foreach item="id" index="index" collection="ids" open="(" separator="," close=")">  
    #{id}  
  </foreach>  
</select>

4, 1bf98fa25b9723947864cac5bc2e4662, 196185dae55b7edbe154a5051db664a7 and ace372f96ca3ec664acb3aaa2421b04c tags: These tags are used to handle extra spaces and commas in SQL statements and generate UPDATE SET clause in the statement. The 1bf98fa25b9723947864cac5bc2e4662 tag can be used to remove extra spaces and commas, the 196185dae55b7edbe154a5051db664a7 tag can be used to generate a WHERE clause, and the ace372f96ca3ec664acb3aaa2421b04c tag can be used to generate the SET clause in an UPDATE statement. For example:

<update id="updateUser" parameterType="User">  
  UPDATE user SET   
  <set>  
    <if test="name != null">name = #{name},</if>  
    <if test="age != null">age = #{age},</if>  
    <!-- 其他属性 -->  
  </set>  
  WHERE id = #{id}  
</update>

5, 94561e999a5eec0e6ba7d7040437c3f1 Tag: 94561e999a5eec0e6ba7d7040437c3f1 tag is used to define variables in XML mapping files and reference the variables in SQL statements. This can be used to build more complex dynamic SQL statements. For example:

<bind id="userWhereClause" parameterType="map">  
  AND name = #{name}  
  AND age = #{age}  
</bind>  
  
<select id="findUserByParams" resultType="User">  
  SELECT * FROM user WHERE 1=1 <include refid="userWhereClause"/>  
</select>

These are commonly used dynamic SQL tags in MyBatis. They can help developers build flexible and dynamic SQL query statements. When using these tags, you need to pay attention to avoid SQL injection attacks and ensure the security of input parameters.

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