/**
 * Copyright &copy; 2012-2016 <a href="https://github.com/thinkgem/jeesite">JeeSite</a> All rights reserved.
 */
package com.thinkgem.jeesite.common.persistence.dialect.db;

import com.thinkgem.jeesite.common.persistence.dialect.Dialect;

/**
 * Postgre Sql的方言实现
 * @author poplar.yfyang
 * @version 1.0 2010-10-10 下午12:31
 * @since JDK 1.5
 */
public class PostgreSQLDialect implements Dialect {

    public boolean supportsLimit() {
        return true;
    }

    @Override
    public String getLimitString(String sql, int offset, int limit) {
        return getLimitString(sql, offset, Integer.toString(offset),
                Integer.toString(limit));
    }

    /**
     * 将sql变成分页sql语句,提供将offset及limit使用占位符号(placeholder)替换.
     * <pre>
     * 如mysql
     * dialect.getLimitString("select * from user", 12, ":offset",0,":limit") 将返回
     * select * from user limit :offset,:limit
     * </pre>
     *
     * @param sql               实际SQL语句
     * @param offset            分页开始纪录条数
     * @param offsetPlaceholder 分页开始纪录条数－占位符号
     * @param limitPlaceholder  分页纪录条数占位符号
     * @return 包含占位符的分页sql
     */
    public String getLimitString(String sql, int offset,
                                 String offsetPlaceholder, String limitPlaceholder) {
        StringBuilder pageSql = new StringBuilder().append(sql);
        pageSql = offset <= 0
                ? pageSql.append(" limit ").append(limitPlaceholder) :
                pageSql.append(" limit ").append(limitPlaceholder).append(" offset ").append(offsetPlaceholder);
        return pageSql.toString();
    }
}
