用insert into select 以及left join给出

您可以使用INSERT INTO SELECT语句和LEFT JOIN来实现多表融合并去掉多余的字段。以下是使用这种方法的示例：

INSERT INTO A (a1, b1)
SELECT A.a1, E.b1
FROM A
LEFT JOIN D ON A.a1 = D.a1
LEFT JOIN E ON A.a1 = E.a1
LEFT JOIN F ON E.b1 = F.b1;

在这个例子中，我们使用了多个LEFT JOIN语句将表D、E和F与表A进行连接。通过LEFT JOIN，即使没有在所有表中找到匹配的记录，也会返回表A中的记录。最终的SELECT子句中，我们只选择了表A和表E中需要的字段a1和b1。然后，将这些字段的值插入到表A中。这样就实现了多表融合并去掉多余的字段。

相关问题

insert into select from left in

对于insert into select from left in这个问题，可以使用以下方法进行处理。首先，我们需要确保语句的正确性和可读性。其次，我们可以使用INSERT INTO SELECT语句来将左连接的结果插入到目标表中。例如，可以使用以下语句:

INSERT INTO table_name_new (column1, column2...)
SELECT column1, column2...
FROM table_name_old
LEFT JOIN tableC ON table_name_old.column = tableC.column

这里，table_name_new是目标表名，column1、column2...是目标表的字段，table_name_old是源表名，column1、column2...是源表的字段。LEFT JOIN语句用于将table_name_old和tableC进行左连接，可以根据需要修改连接条件。

需要注意的是，在使用INSERT INTO SELECT语句时，要确保源表和目标表的结构一致，以便正确地插入数据。同时，还要确保相关的条件和索引设置正确，以避免出现数据被锁定的情况。

以下是使用Java和druid解析sql，并通过feign接口查询到的表元数据，替换包含left join的insert into table select sql语句中的*的代码示例：

以下是使用Java和druid解析sql，并通过feign接口查询到的表元数据，替换包含left join的insert into table select sql语句中的*的代码示例：

import com.alibaba.druid.sql.SQLUtils;
import com.alibaba.druid.sql.ast.SQLExpr;
import com.alibaba.druid.sql.ast.SQLStatement;
import com.alibaba.druid.sql.ast.expr.SQLIdentifierExpr;
import com.alibaba.druid.sql.ast.statement.*;
import com.alibaba.druid.util.JdbcConstants;
import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;
import com.google.common.base.Joiner;
import feign.Feign;
import feign.gson.GsonDecoder;
import feign.gson.GsonEncoder;
import feign.okhttp.OkHttpClient;
import feign.slf4j.Slf4jLogger;
import lombok.extern.slf4j.Slf4j;
import org.springframework.util.CollectionUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

@Slf4j
public class SqlParserUtils {

    /**
     * 解析insert into table select语句中的表名
     */
    public static String parseTableName(String sql) {
        List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, JdbcConstants.MYSQL);
        SQLInsertStatement insertStmt = (SQLInsertStatement) stmtList.get(0);
        SQLSelectStatement selectStmt = (SQLSelectStatement) insertStmt.getQuery().getQuery();
        SQLSelect sqlSelect = selectStmt.getSelect();
        SQLSelectQueryBlock sqlSelectQuery = (SQLSelectQueryBlock) sqlSelect.getQuery();
        SQLTableSource tableSource = sqlSelectQuery.getFrom();
        if (tableSource instanceof SQLExprTableSource) {
            return ((SQLExprTableSource) tableSource).getName().getSimpleName();
        } else if (tableSource instanceof SQLJoinTableSource) {
            SQLJoinTableSource joinSource = (SQLJoinTableSource) tableSource;
            SQLTableSource left = joinSource.getLeft();
            if (left instanceof SQLExprTableSource) {
                return ((SQLExprTableSource) left).getName().getSimpleName();
            }
        }
        throw new IllegalArgumentException("无法解析的SQL语句");
    }

    /**
     * 解析insert into table select语句中的列名
     */
    public static List<String> parseColumnNames(String sql) {
        List<SQLStatement> stmtList = SQLUtils.parseStatements(sql, JdbcConstants.MYSQL);
        SQLInsertStatement insertStmt = (SQLInsertStatement) stmtList.get(0);
        SQLSelectStatement selectStmt = (SQLSelectStatement) insertStmt.getQuery().getQuery();
        SQLSelect sqlSelect = selectStmt.getSelect();
        SQLSelectQueryBlock sqlSelectQuery = (SQLSelectQueryBlock) sqlSelect.getQuery();
        List<SQLSelectItem> selectList = sqlSelectQuery.getSelectList();
        List<String> columnNames = new ArrayList<>();
        for (SQLSelectItem selectItem : selectList) {
            SQLExpr expr = selectItem.getExpr();
            if (expr instanceof SQLIdentifierExpr) {
                columnNames.add(((SQLIdentifierExpr) expr).getName());
            }
        }
        return columnNames;
    }

    /**
     * 替换insert into table select语句中的*为实际列名
     */
    public static String replaceAsterisk(String sql, List<String> columnNames) {
        SQLSelectParser parser = new MySqlSelectParser(sql);
        SQLSelect select = parser.select();
        SQLSelectQueryBlock query = (SQLSelectQueryBlock) select.getQuery();
        List<SQLSelectItem> selectList = query.getSelectList();
        if (!CollectionUtils.isEmpty(selectList)) {
            for (int i = 0; i < selectList.size(); i++) {
                SQLSelectItem selectItem = selectList.get(i);
                SQLExpr expr = selectItem.getExpr();
                if (expr instanceof SQLAllColumnExpr) {
                    selectList.remove(i);
                    for (String columnName : columnNames) {
                        SQLSelectItem newSelectItem = new SQLSelectItem(new SQLIdentifierExpr(columnName));
                        selectList.add(i, newSelectItem);
                        i++;
                    }
                    break;
                }
            }
        }
        return SQLUtils.toMySqlString(select);
    }

    /**
     * 查询表元数据
     */
    public static JSONObject getTableMetadata(String tableName, String metadataServiceUrl) {
        Feign.Builder builder = Feign.builder()
                .encoder(new GsonEncoder())
                .decoder(new GsonDecoder())
                .logger(new Slf4jLogger(SqlParserUtils.class))
                .client(new OkHttpClient());
        MetadataServiceClient client = builder.target(MetadataServiceClient.class, metadataServiceUrl);
        Map<String, Object> result = client.getTableMetadata(tableName);
        return JSON.parseObject(JSON.toJSONString(result));
    }

    /**
     * 替换insert into table select语句中的*为实际列名，并获取列的类型信息
     */
    public static String replaceAsteriskAndGetType(String sql, String metadataServiceUrl) {
        String tableName = parseTableName(sql);
        List<String> columnNames = parseColumnNames(sql);
        JSONObject tableMetadata = getTableMetadata(tableName, metadataServiceUrl);
        List<JSONObject> columns = tableMetadata.getJSONArray("columns").toJavaList(JSONObject.class);
        List<String> columnTypes = columns.stream().filter(column -> columnNames.contains(column.getString("name")))
                .map(column -> column.getString("type")).collect(Collectors.toList());
        String replacedSql = replaceAsterisk(sql, columnNames);
        String columnTypesStr = Joiner.on(",").join(columnTypes);
        return String.format("%s/*{%s}*/", replacedSql, columnTypesStr);
    }

}

其中，MetadataServiceClient为通过Feign实现的调用元数据服务接口的客户端，代码示例如下：

import feign.RequestLine;

import java.util.Map;

public interface MetadataServiceClient {

    @RequestLine("GET /metadata/tables/{tableName}")
    Map<String, Object> getTableMetadata(String tableName);

}