这个Java类 SqlTemplate 主要用于定义和存储SQL查询模板字符串，这些模板字符串使用StringTemplate库的语法编写。以下是类的主要功能和特点的概要描述：
- 类包含两个静态常量字符串：
QUERY_SQL和PREVIEW_SQL，它们分别定义了两种不同的SQL查询模板。 QUERY_SQL模板用于生成标准的SQL查询语句，包括选择字段、表名、别名、WHERE条件、GROUP BY子句、ORDER BY子句等。PREVIEW_SQL模板用于生成预览数据的SQL查询语句，它与QUERY_SQL类似，但可能包含一些特定的预览相关的逻辑，如去重（DISTINCT）等。- 模板使用StringTemplate的语法，允许通过传入参数动态地构建SQL查询语句。
- 模板中包含了条件判断（如
<if(condition)>），可以根据传入的参数值决定是否包含特定的SQL片段。 - 模板支持循环（如
<groups:{group|...}; separator=",">），可以迭代传入的列表参数，为每个元素生成相应的SQL片段。 - 模板字符串是硬编码的，意味着它们在编译时就已经确定，并且不会在运行时改变。
- 这些模板可以在
SQLProvider类中使用，通过填充具体的参数来生成完整的SQL查询语句。 - 模板的设计使得SQL语句的构建更加灵活和可维护，同时也减少了代码重复，并提高了生成SQL语句的效率。
package io.dataease.engine.sql;
/**
* @Author Junjun
*/
public class SqlTemplate {
public static String QUERY_SQL = "querySql(limitFiled, groups, aggregators, filters, orders, table, notUseAs, useAliasForGroup)n"
"::=<<n"
"SELECTn"
"<if(limitFiled)>n"
" <limitFiled.limitFiled>n"
"<endif>n"
"<if(!groups && !aggregators)>n"
" *n"
"<endif>n"
"<if(groups && notUseAs)>n"
" <groups:{group|<if(group)><group.fieldName> <endif>}; separator=",\n">n"
"<endif>n"
"<if(groups && !notUseAs)>n"
" <groups:{group|<if(group)><group.fieldName> AS <group.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
" <if(groups && aggregators)>,<endif>n"
"<if(aggregators)>n"
" <aggregators:{agg|<if(agg)><agg.fieldName> AS <agg.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
"FROMn"
" <table.tableName> <table.tableAlias>n"
"<if(filters)>n"
"WHEREn"
" <filters:{filter|<if(filter)><filter><endif>}; separator="\nAND ">n"
"<endif>n"
"<if(groups && !useAliasForGroup)>n"
"GROUP BYn"
" <groups:{group|<if(group)><group.fieldName><endif>}; separator=",\n">n"
"<endif>n"
"<if(groups && useAliasForGroup)>n"
"GROUP BYn"
" <groups:{group|<if(group)><group.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
"<if(orders)>n"
"ORDER BYn"
" <orders:{order|<if(order)><order.orderAlias> <order.orderDirection><endif>}; separator=",\n">n"
"<endif>n"
">>";
public static String PREVIEW_SQL = "previewSql(limitFiled, groups, aggregators, filters, orders, table, isGroup, notUseAs, useAliasForGroup, distinct)n"
"::=<<n"
"SELECTn"
"<if(limitFiled)>n"
" <limitFiled.limitFiled>n"
"<endif>n"
"<if(!groups && !aggregators)>n"
" *n"
"<endif>n"
"<if(groups && notUseAs)>n"
" <groups:{group|<if(group)><group.fieldName> <endif>}; separator=",\n">n"
"<endif>n"
"<if(groups && !notUseAs)>n"
" <groups:{group|<if(group)><if(distinct)> DISTINCT <endif> <group.fieldName> AS <group.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
" <if(groups && aggregators)>,<endif>n"
"<if(aggregators)>n"
" <aggregators:{agg|<if(agg)><agg.fieldName> AS <agg.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
"FROMn"
" <table.tableName> <table.tableAlias>n"
"<if(filters)>n"
"WHEREn"
" <filters:{filter|<if(filter)><filter><endif>}; separator="\nAND ">n"
"<endif>n"
"<if(isGroup && groups && !useAliasForGroup)>n"
"GROUP BYn"
" <groups:{group|<if(group)><group.fieldName><endif>}; separator=",\n">n"
"<endif>n"
"<if(isGroup && groups && useAliasForGroup)>n"
"GROUP BYn"
" <groups:{group|<if(group)><group.fieldAlias><endif>}; separator=",\n">n"
"<endif>n"
"<if(orders)>n"
"ORDER BYn"
" <orders:{order|<if(order)><order.orderAlias> <order.orderDirection><endif>}; separator=",\n">n"
"<endif>n"
">>";
}
