优化两个select count查询，当表只有一个主键的时候，使用select count(pk)，其他时候使用select count(*)

abel533 · abel533 · commit 5b94a2d65f40 · 2016-01-11T20:33:16.000+08:00
diff --git a/README.md b/README.md
@@ -112,7 +112,7 @@ http://repo1.maven.org/maven2/javax/persistence/persistence-api/1.0/
 
 * `Example`增加对动态表名支持，通过`setTableName`设置表名
 * 在example相关的两个`update`方法中，参数为实体类和`Example`，这个方法只能通过`Example`来设置动态表名，不支持通过实体设置动态表名
-
+* 优化两个`select count`查询，当表只有一个主键的时候，使用`select count(pk)`，其他时候使用`select count(*)`
 
 ###3.3.4 - 2016-01-05
 
diff --git a/pom.xml b/pom.xml
@@ -28,7 +28,7 @@
 
     <groupId>tk.mybatis</groupId>
     <artifactId>mapper</artifactId>
-    <version>3.3.5</version>
+    <version>3.3.5-SNAPSHOT</version>
     <packaging>jar</packaging>
 
     <name>mapper</name>
diff --git a/src/main/java/tk/mybatis/mapper/mapperhelper/SqlHelper.java b/src/main/java/tk/mybatis/mapper/mapperhelper/SqlHelper.java
@@ -251,6 +251,24 @@ public static String selectAllColumns(Class<?> entityClass) {
         return sql.toString();
     }
 
+    /**
+     * select count(x)
+     *
+     * @param entityClass
+     * @return
+     */
+    public static String selectCount(Class<?> entityClass) {
+        StringBuilder sql = new StringBuilder();
+        sql.append("SELECT ");
+        Set<EntityColumn> pkColumns = EntityHelper.getPKColumns(entityClass);
+        if (pkColumns.size() == 1) {
+            sql.append("COUNT(").append(pkColumns.iterator().next().getColumn()).append(") ");
+        } else {
+            sql.append("COUNT(*) ");
+        }
+        return sql.toString();
+    }
+
     /**
      * from tableName - 动态表名
      *
diff --git a/src/main/java/tk/mybatis/mapper/provider/ExampleProvider.java b/src/main/java/tk/mybatis/mapper/provider/ExampleProvider.java
@@ -48,7 +48,8 @@ public ExampleProvider(Class<?> mapperClass, MapperHelper mapperHelper) {
      */
     public String selectCountByExample(MappedStatement ms) {
         Class<?> entityClass = getEntityClass(ms);
-        StringBuilder sql = new StringBuilder("SELECT COUNT(*) ");
+        StringBuilder sql = new StringBuilder();
+        sql.append(SqlHelper.selectCount(entityClass));
         sql.append(SqlHelper.fromTable(entityClass, tableName(entityClass)));
         sql.append(SqlHelper.exampleWhereClause());
         return sql.toString();
diff --git a/src/main/java/tk/mybatis/mapper/provider/base/BaseSelectProvider.java b/src/main/java/tk/mybatis/mapper/provider/base/BaseSelectProvider.java
@@ -110,7 +110,7 @@ public String selectByPrimaryKey(MappedStatement ms) {
     public String selectCount(MappedStatement ms) {
         Class<?> entityClass = getEntityClass(ms);
         StringBuilder sql = new StringBuilder();
-        sql.append("SELECT COUNT(*) ");
+        sql.append(SqlHelper.selectCount(entityClass));
         sql.append(SqlHelper.fromTable(entityClass, tableName(entityClass)));
         sql.append(SqlHelper.whereAllIfColumns(entityClass, isNotEmpty()));
         return sql.toString();
