SQL知识点合集---第二弹
数据一
<select id="listPositionAuditCheckSample" resultType="net.nxe.cloud.content.server.entity.PositionAuditCheckSample"><trim prefixOverrides="union all"><if test="userSampleCount != null and userSampleCount > 0">select pat.position_id position_id, pat.id audit_idfrom (select t.creator,cast(concat('[',substring_index(group_concat(concat('"', t.audit_id, '"') order by rand()),',',#{userSampleCount}),']') as json) audit_idsfrom (select pat.position_id, max(pat.id) audit_id, pat.creatorfrom position_audit patwhere pat.creator > 1and pat.entry in ('AUDITING', 'RECHECKING')and pat.create_time between #{startDate} and date_add(#{endDate}, interval 86399 second)and pat.creator in (<foreach collection="auditors" item="auditor" separator=",">#{auditor}</foreach>)and pat.finished = 1 and pat.id = pat.`group`group by pat.position_id, pat.creator, date_format(pat.create_time, '%Y-%m-%d')) tinner join position pn on pn.id = t.position_id and pn.updater = t.creator and pn.source = 'USER'group by t.creator) tinner join position_audit pat on pat.creator = t.creatorand json_contains(t.audit_ids, concat('"', pat.id, '"'))</if><if test="captureExactSampleCount != null and captureExactSampleCount > 0">union allselect pat.position_id position_id, pat.id audit_idfrom (select t.creator,cast(concat('[',substring_index(group_concat(concat('"', t.audit_id, '"') order by rand()),',',#{captureExactSampleCount}),']') as json) audit_idsfrom (select pat.position_id, max(pat.id) audit_id, pat.creatorfrom position_audit patwhere pat.creator > 1and pat.entry in ('AUDITING', 'RECHECKING')and pat.create_time between #{startDate} and date_add(#{endDate}, interval 86399 second)and pat.creator in (<foreach collection="auditors" item="auditor" separator=",">#{auditor}</foreach>)and pat.finished = 1 and pat.id = pat.`group`group by pat.position_id, pat.creator, date_format(pat.create_time, '%Y-%m-%d')) tinner join position pnon pn.id = t.position_id and pn.updater = t.creator and pn.source = 'CAPTURED' and `vague` = 0group by t.creator) tinner join position_audit pat on pat.creator = t.creatorand json_contains(t.audit_ids, concat('"', pat.id, '"'))</if><if test="captureVagueSampleCount != null and captureVagueSampleCount > 0">union allselect pat.position_id position_id, pat.id audit_idfrom (select t.creator,cast(concat('[',substring_index(group_concat(concat('"', t.audit_id, '"') order by rand()),',',#{captureVagueSampleCount}),']') as json) audit_idsfrom (select pat.position_id, max(pat.id) audit_id, pat.creatorfrom position_audit patwhere pat.creator > 1and pat.entry in ('AUDITING', 'RECHECKING')and pat.create_time between #{startDate} and date_add(#{endDate}, interval 86399 second)and pat.creator in (<foreach collection="auditors" item="auditor" separator=",">#{auditor}</foreach>)and pat.finished = 1 and pat.id = pat.`group`group by pat.position_id, pat.creator, date_format(pat.create_time, '%Y-%m-%d')) tinner join position pnon pn.id = t.position_id and pn.updater = t.creator and pn.source = 'CAPTURED' and `vague` = 1group by t.creator) tinner join position_audit pat on pat.creator = t.creatorand json_contains(t.audit_ids, concat('"', pat.id, '"'))</if></trim></select>知识点
<trim>标签的使用
-
作用：去除 SQL 片段开头多余的
UNION ALL。 -
示例：
<trim prefixOverrides="union all"><if>...</if><if>...</if>
</trim>-
说明：如果第一个
<if>条件不满足，生成的 SQL 不会以UNION ALL开头，避免语法错误。
GROUP_CONCAT + ORDER BY RAND()
-
作用：将多个值拼接成字符串，并按随机顺序排序。
-
示例：
group_concat(concat('"', t.audit_id, '"') order by rand())SUBSTRING_INDEX
-
作用：截取字符串的前 N 个元素。
-
示例：
substring_index(group_concat(...), ',', #{userSampleCount})CAST(... AS JSON)
-
作用：将字符串转换为 MySQL 的 JSON 类型。
-
示例：
cast(concat('[', substring_index(...), ']') as json)JSON_CONTAIN
-
作用：检查 JSON 数组中是否包含某个值。
-
示例：
json_contains(t.audit_ids, concat('"', pat.id, '"'))JSON数据类型处理
| 函数 | 作用 | 示例场景 |
|---|---|---|
JSON_ARRAY() | 创建 JSON 数组 | 初始化订单状态历史 |
JSON_ARRAY_APPEND() | 向数组追加元素 | 添加新状态 |
JSON_LENGTH() | 获取数组/对象长度 | 限制状态历史长度 |
JSON_MERGE_PATCH() | 合并并覆盖重复键（对象） | 更新物流信息 |
JSON_EXTRACT() | 提取 JSON 中的值 | 查询最新状态 |
JSON_CONTAINS_PATH() | 检查 JSON 中是否存在指定路径 | 验证物流信息是否存在 |
JSON_MERGE() | 合并 JSON 文档（兼容旧版本） | 合并用户备注（注意数组行为） |
CREATE TABLE orders (order_id INT PRIMARY KEY AUTO_INCREMENT,user_id INT NOT NULL,status_history JSON COMMENT '状态变更历史（JSON数组）',extra_info JSON COMMENT '额外信息（JSON对象）'
);-- JSON_ARRAY()、JSON_OBJECT
INSERT INTO orders (user_id, status_history, extra_info)
VALUES (1001,JSON_ARRAY('created'), JSON_OBJECT('note', '请尽快发货')
);-- JSON_ARRAY_APPEND：追加数据
UPDATE orders
SET status_history = JSON_ARRAY_APPEND(status_history, '$', 'ios')
WHERE order_id = 1;-- JSON_MERGE_PATCH：追加数据
UPDATE orders
SET extra_info = JSON_MERGE_PATCH(extra_info,'{"logistics": {"company": "顺丰", "tracking_no": "SF123456"}}'
)
WHERE order_id = 1;-- JSON_EXTRACT() 提取最后一个状态
SELECTJSON_EXTRACT(status_history, '$[last]') AS last_status
FROM orders
WHERE order_id = 1;-- JSON_CONTAINS_PATH() 验证extra_info中是否有物流信息
SELECTJSON_CONTAINS_PATH(extra_info, 'one', '$.logistics') AS has_logistics
FROM orders
WHERE order_id = 1;-- JSON_MERGE：会合并为数组
UPDATE orders
SET extra_info = JSON_MERGE(extra_info,'{"note": "已加急处理"}'
)
WHERE order_id = 1;-- JSON_LENGTH()长度
SELECT * from orders where JSON_LENGTH(status_history)>2