sql 查询判断语句
    英文回答：
    In SQL, we can use the SELECT statement to query and retrieve data from a database. The SELECT statement is followed by a list of columns we want to retrieve data from, and the FROM clause specifies the table(s) we want to retrieve data from. We can also use the WHERE clause to add conditions to filter the data based on specific criteria.
    For example, let's say we have a table called "employees" with columns such as "employee_id", "first_name", "last_name", and "salary". If we want to retrieve the first name and last name of all employees with a salary greater than 5000, we can use the following SQL query:
    SELECT first_name, last_name.
    FROM employees.
    WHERE salary > 5000;
    This query will return the first name and last name of all employees whose salary is greater than 5000.
    Now, let's say we want to retrieve the first name, last name, and salary of all employees with a salary greater than 5000 and who are from the "Sales" department. We can use the following SQL query:
    SELECT first_name, last_name, salary.
    FROM employees.
    WHERE salary > 5000。
    AND department = 'Sales';
    This query will return the first name, last name, and salary of all employees whose salary is greater than 5000 and who belong to the "Sales" department.
    In addition to the WHERE clause, we can also use other operators such as LIKE, IN, BE
TWEEN, and NOT to add more complex conditions to our SQL queries. For example, we can use the LIKE operator to retrieve all employees whose last name starts with "S":
    SELECT first_name, last_name.
    FROM employees.
    WHERE last_name LIKE 'S%';
sql语句怎么查询两张表的数据
    This query will return the first name and last name of all employees whose last name starts with "S".
    中文回答：
    在SQL中，我们可以使用SELECT语句从数据库中查询和检索数据。SELECT语句后面跟着我们想要从中检索数据的列的列表，FROM子句指定我们想要从中检索数据的表。我们还可以使用WHERE子句根据特定条件添加过滤数据的条件。
    例如，假设我们有一个名为“employees”的表，其中包含“employee_id”，“first_name”，“la
st_name”和“salary”等列。如果我们想要检索所有工资大于5000的员工的名字和姓氏，我们可以使用以下SQL查询：
    SELECT first_name, last_name.
    FROM employees.
    WHERE salary > 5000;
    这个查询将返回所有工资大于5000的员工的名字和姓氏。
    现在，假设我们想要检索工资大于5000并且来自“Sales”部门的所有员工的名字、姓氏和工资。我们可以使用以下SQL查询：
    SELECT first_name, last_name, salary.
    FROM employees.
    WHERE salary > 5000。
    AND department = 'Sales';
    这个查询将返回工资大于5000并且属于“Sales”部门的所有员工的名字、姓氏和工资。
    除了WHERE子句之外，我们还可以使用其他运算符，如LIKE、IN、BETWEEN和NOT，来为我们的SQL查询添加更复杂的条件。例如，我们可以使用LIKE运算符来检索所有姓氏以“S”开头的员工：
    SELECT first_name, last_name.
    FROM employees.
    WHERE last_name LIKE 'S%';
    这个查询将返回所有姓氏以“S”开头的员工的名字和姓氏。

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