com.baomidou.mybatisplus.extension.plugins.pagination.dialects.SybaseDialect Maven / Gradle / Ivy

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/*
 * Copyright (c) 2011-2023, baomidou ([email protected]).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.baomidou.mybatisplus.extension.plugins.pagination.dialects;

import com.baomidou.mybatisplus.extension.plugins.pagination.DialectModel;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * sybase 数据库分页方言
 *
 * @author sdsyjh
 * @since 2020-07-30
 */
public class SybaseDialect implements IDialect {

    private final boolean hasTop; // sybase12.5.4以前，不支持select top

    public SybaseDialect() {
        this(false);
    }

    public SybaseDialect(boolean hasTop) {
        this.hasTop = hasTop;
    }

    @Override
    public DialectModel buildPaginationSql(String originalSql, long offset, long limit) {
        int index = findMainFROM(originalSql);
        if(index == -1){
            index = originalSql.toUpperCase().indexOf(" FROM ");
        }
        String sql = "select";
        if (hasTop) {
            sql += " top " + (offset + limit);
        }
        sql += " rownum=identity(12)," + originalSql.substring(6, index) + " into #t " + originalSql.substring(index);
        sql += " select * from #t where rownum > ? and rownum <= ? ";
        sql += "drop table #t ";
        return new DialectModel(sql, offset, offset + limit).setConsumerChain();
    }

    /**
     * 查找主查询的FROM位置
     * @param sql   需要查找的SQL
     * @return  FROM位置的起始下标
     * @author lroyia
     * @since  2022年6月15日 17:57:28
     */
    private int findMainFROM(String sql){
        String tempSql = sql.toUpperCase();
        tempSql = tempSql.replace("\n", " ").replace("\t", " ").replace("\r", " ");
        Matcher select_ = Pattern.compile("SELECT ").matcher(tempSql);
        Matcher from_ = Pattern.compile(" FROM ").matcher(tempSql);
        List selectIndex = new ArrayList<>(10);
        List fromIndex = new ArrayList<>(10);
        while (select_.find()){
            int start = select_.start();
            if(start == 0 || tempSql.charAt(start - 1) == ' '|| tempSql.charAt(start - 1) == '('){
                selectIndex.add(start);
            }
        }
        while (from_.find()){
            fromIndex.add(from_.start());
        }

        // 形成select与from的混合顺序下标列表
        List indexList = new ArrayList<>(20);
        indexList.addAll(selectIndex);
        indexList.addAll(fromIndex);
        indexList.sort(Comparator.naturalOrder());
        // 无法匹配有效下标
        if(indexList.size() < 2){
            return -1;
        }
        // 利用栈逻辑匹配select与from
        int selectCount = 1;
        for(int i = 1; i < indexList.size(); i++){
            int each = indexList.get(i);
            if(fromIndex.contains(each)){
                // pointer弹栈
                selectCount--;
            }else{
                // pointer压栈
                selectCount++;
            }
            // from将全部select弹出，代表当前这个from为主要from
            if(selectCount == 0){
                return each;
            }
        }
        return -1;
    }
}