SELECT
*
FROM table
SELECT
name,
age,
eyes_color
FROM bbdd
SELECT DISTINCT
column_1
FROM table
SELECT DISTINCT
eyes_colors
FROM bbdd
SELECT
*
FROM table
WHERE column_1 = "Given Condition"
SELECT DISTINCT
*
FROM bbdd
WHERE eyes_color = "Blue"
SELECT
*
FROM bbdd
WHERE eyes_color = "Blue"
AND age < 20
SELECT
*
FROM bbdd
WHERE eyes_color = "Blue"
OR eyes_color = "Green"
SELECT
*
FROM table
ORDER BY column1 ASC/DESC
SELECT
*
FROM bbdd
ORDER BY age DESC
SELECT
*
FROM bbdd
ORDER BY eyes_color, age DESC
COUNT() 返回总行数。通常与 DISTINCT 命令一起使用以计算唯一元素。 SUM() 返回所有值的总和 MAX() 返回最大值 MIN() 返回最小值 AVG() 返回平均值
SELECT
COUNT(*)
FROM bbdd
SELECT
COUNT(DISTINCT eyes_color)
FROM bbdd
SELECT
eyes_color,
COUNT(*)
FROM bbdd
GROUP BY eyes_color
SELECT
*
FROM bbdd
WHERE eyes_color = "Blue"
UNION
SELECT
*
FROM bbdd
WHERE eyes_color = "Brown"
UNION
SELECT
*
FROM bbdd
WHERE eyes_color = "Green"
重命名列
SELECT
column_1 AS new_name
FROM bbdd
重命名表
SELECT
A.age
FROM bbdd as A
CASE WHEN——如果满足条件。 THEN——做这个。 ELSE — 否则做其他事情。
SELECT
*,
CASE WHEN age < 20 THEN "teen"
WHEN age >= 20 AND age < 30 THEN "youngster"
ELSE THEN "adult"
END AS type
FROM bbdd
INNER JOIN— 语句仅返回那些具有匹配值的记录或行，用于检索出现在两个表中的数据。
LEFT JOIN — 按照左表的结构给出两个表之间匹配行的输出。如果左表中没有记录匹配，它会显示那些具有空值的记录。
CROSS JOIN—返回每个表中行的所有组合。请注意，此连接不需要任何条件来连接两个表。
SELECT
T1.name,
T1.age,
T1.eyes_color,
T2.gender
FROM bbdd AS T1
LEFT JOIN bbdd_gender AS T2
ON T1.name = T2.name
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