(一)、根据teacher_no统计星期的上课数
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-- 解法一
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SELECT
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t1.teacher_no,
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(CASE WEEK WHEN '1' THEN keshu ELSE 0 END ) 礼拜一,
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(CASE WEEK WHEN '2' THEN keshu ELSE 0 END ) 礼拜二,
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(CASE WEEK WHEN '3' THEN keshu ELSE 0 END ) 礼拜三
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FROM
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(
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SELECT
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teacher_no,
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WEEK,
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COUNT(1) AS keshu
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FROM teach
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GROUP BY teacher_no,WEEK
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)t1
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GROUP BY t1.teacher_no;
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-- 解法二 就是count()函数作用
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SELECT
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t1.teacher_no,
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(CASE WEEK WHEN '1' THEN keshu ELSE 0 END ) 礼拜一,
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(CASE WEEK WHEN '2' THEN keshu ELSE 0 END ) 礼拜二,
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(CASE WEEK WHEN '3' THEN keshu ELSE 0 END ) 礼拜三
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FROM
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(
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SELECT
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t.teacher_no,
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t.WEEK,
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COUNT(t.keshu) AS keshu
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FROM
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(
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SELECT
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teacher_no,
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WEEK,
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'1' keshu
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FROM teach )t
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GROUP BY teacher_no,WEEK
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)t1
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GROUP BY t1.teacher_no
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