1. SELECT COUNT(*) FROM teacher WHERE Tname LIKE '李%'
    SELECT
    student.* 
FROM
    student,
    sc 
WHERE
    student.SId = sc.SId 
    AND sc.CId = (
    SELECT
        CId 
    FROM
        course 
    WHERE
    TId = ( SELECT TId FROM teacher WHERE Tname = '张三' ))