如何在Oracle中将多个表中的数据插入到一个表中？

INSERT INTO target_table (column1, column2, column3)
SELECT column1, column2, column3 FROM table1
UNION ALL
SELECT column1, column2, column3 FROM table2
UNION ALL
SELECT column1, column2, column3 FROM table3;

INSERT INTO target_table (column1, column2, column3)
SELECT column1, column2, column3
FROM (
    SELECT column1, column2, column3 FROM table1
    UNION ALL
    SELECT column1, column2, column3 FROM table2
    UNION ALL
    SELECT column1, column2, column3 FROM table3
);

DECLARE
    l_sql_stmt VARCHAR2(200);
BEGIN
    l_sql_stmt := 'INSERT INTO target_table (column1, column2, column3)
                   SELECT column1, column2, column3 FROM table1';
    DBMS_PARALLEL_EXECUTE.CREATE_TASK ('task1');
    DBMS_PARALLEL_EXECUTE.RUN_TASK ('task1', l_sql_stmt, 4);
    DBMS_PARALLEL_EXECUTE.DROP_TASK ('task1');

    l_sql_stmt := 'INSERT INTO target_table (column1, column2, column3)
                   SELECT column1, column2, column3 FROM table2';
    DBMS_PARALLEL_EXECUTE.CREATE_TASK ('task2');
    DBMS_PARALLEL_EXECUTE.RUN_TASK ('task2', l_sql_stmt, 4);
    DBMS_PARALLEL_EXECUTE.DROP_TASK ('task2');

    l_sql_stmt := 'INSERT INTO target_table (column1, column2, column3)
                   SELECT column1, column2, column3 FROM table3';
    DBMS_PARALLEL_EXECUTE.CREATE_TASK ('task3');
    DBMS_PARALLEL_EXECUTE.RUN_TASK ('task3', l_sql_stmt, 4);
    DBMS_PARALLEL_EXECUTE.DROP_TASK ('task3');
END;
/

CREATE TABLE external_table (
    column1 VARCHAR2(50),
    column2 VARCHAR2(50),
    column3 VARCHAR2(50)
) ORGANIZATION EXTERNAL (
    TYPE ORACLE_LOADER
    DEFAULT DIRECTORY ext_dir
    ACCESS PARAMETERS (
        RECORDS DELIMITED BY NEWLINE
        FIELDS TERMINATED BY ','
    )
    LOCATION ('data.csv')
);

INSERT INTO target_table (column1, column2, column3)
SELECT column1, column2, column3 FROM external_table;

INSERT INTO target_table (column1, column2, column3)
SELECT CAST(column1 AS VARCHAR2(50)), column2, column3 FROM table1;

MERGE INTO target_table t
USING (
    SELECT column1, column2, column3 FROM table1
    UNION ALL
    SELECT column1, column2, column3 FROM table2
    UNION ALL
    SELECT column1, column2, column3 FROM table3
) s
ON (t.column1 = s.column1)
WHEN MATCHED THEN
    UPDATE SET t.column2 = s.column2, t.column3 = s.column3
WHEN NOT MATCHED THEN
    INSERT (column1, column2, column3) VALUES (s.column1, s.column2, s.column3);