mysql - sql 复合键帮助

Question

使用 sql，我需要将 Lineno 和 orderline 变成一个复合键我该怎么做，到目前为止我已经有了

CREATE TABLE ORDERLINE (
   ORDERNO INTEGER NOT NULL, 
   LINENO VARCHAR(4) NOT NULL, 
   NUMBERORDERED NUMERIC DEFAULT '1', 
   QUOTEDPRICE NUMERIC DEFAULT '0.00', 
   CONSTRAINT ORDERLINE_ORDERNO_PK PRIMARY KEY (ORDERNO), 
   CONSTRAINT ORDERLINE_ORDERNO_CC CHECK (ORDERNO BETWEEN 10000 AND 99999), 
   CONSTRAINT ORDERLINE_NUMBERORDERED CHECK (NUMBERORDERED BETWEEN 1 AND 100) 
);

Answer 1

CREATE TABLE ORDERLINE (
    ORDERNO INTEGER NOT NULL,
    LINENO VARCHAR(4) NOT NULL,
    NUMBERORDERED NUMERIC DEFAULT '1',
    QUOTEDPRICE NUMERIC DEFAULT '0.00',
    CONSTRAINT ORDERLINE_ORDERNO_PK PRIMARY KEY(ORDERNO, LINENO), -- note alteration on this line
    CONSTRAINT ORDERLINE_ORDERNO_CC CHECK (ORDERNO BETWEEN 10000 AND 99999),
    CONSTRAINT ORDERLINE_NUMBERORDERED CHECK (NUMBERORDERED BETWEEN 1 AND 100)
);

你非常接近。请注意上面添加的列名。

确定哪个字段更有可能成为任何查询中的前导列并将其放在首位。例如;如果您经常通过 OrderNO、LineNo 访问，那将是最好的订单，如果您通过 LineNo、OrderNO 访问该订单。