SELECT e.*, d.* FROM employees e INNER JOIN departments d ON e.department_id = d.department_id;用嵌套怎么写

可以使用子查询来实现这个查询，示例代码如下：

SELECT *
FROM (
    SELECT e.*, d.*
    FROM employees e
    INNER JOIN departments d ON e.department_id = d.department_id
) AS subquery;

在这个示例中，我们首先将原始查询封装在一个子查询中，然后将子查询作为表格调用。这将返回与原始查询相同的结果，但使用了嵌套查询。

相关问题

优化一下sql语句：SELECT * FROM departments WHERE id IN (SELECT d.id , COUNT(*) FROM departments d LEFT JOIN employees e ON d.id = e.Departmentld GROUP BY d.id HAVING COUNT(*) >=10)

好的，我可以帮您优化这条 SQL 查询语句。这个查询主要是找到部门中人员数量大于等于10的部门信息。我建议使用 INNER JOIN 替换子查询的方式，可以提高执行效率并且会返回期望的结果。以下是优化后的 SQL 语句：

SELECT d.* 
FROM departments d 
INNER JOIN (SELECT Departmentld, COUNT(*) as emp_count 
            FROM employees 
            GROUP BY Departmentld 
            HAVING COUNT(*) >= 10) e 
ON d.id = e.Departmentld;

这样优化后的 SQL 查询语句将 JOIN 子查询的结果，省去了子查询的所有记录，大大优化了查询效率。希望这个答案能够帮助到您。

优化sql：SELECT we.organization_id ,we.wip_entity_id ,case when wl.line_id is null then we.wip_entity_name else '' end wip_entity_name ,we.primary_item_id ,mtt.transaction_type_name ,mmt.transaction_date ,bd.department_code ,mmt.inventory_item_id ,mmt.subinventory_code ,mta.reference_account ,br.resource_code ,lu2.meaning as line_type_name ,mta.base_transaction_value ,mta.cost_element_id ,flv.meaning as cost_element ,wdj.class_code job_type_code ,ml.meaning job_type_name FROM (select * from gerp.mtl_material_transactions where substr(transaction_date,1,7) >= '2023-06' and transaction_source_type_id = 5) mmt inner join gerp.wip_entities we on mmt.organization_id = we.organization_id inner join gerp.mtl_transaction_accounts mta on mta.transaction_source_id = we.wip_entity_id and mta.transaction_id = mmt.transaction_id and mta.transaction_source_type_id = 5 inner join gerp.mtl_transaction_types mtt on mtt.transaction_type_id = mmt.transaction_type_id inner join mfg_lookups lu2 on lu2.lookup_code = mta.accounting_line_type and lu2.lookup_type = 'CST_ACCOUNTING_LINE_TYPE' inner join gerp.mtl_system_items_b msi on msi.inventory_item_id = mmt.inventory_item_id and msi.organization_id = mta.organization_id left join gerp.bom_departments bd on bd.department_id = mmt.department_id left join gerp.bom_resources br on br.resource_id = mta.resource_id left join gerp.wip_lines wl on wl.line_id = mmt.repetitive_line_id left join gerp.wip_discrete_jobs wdj on wdj.wip_entity_id = mta.transaction_source_id left join gerp.fnd_lookup_values_vl flv on cast(mta.cost_element_id as string) = flv.lookup_code and flv.lookup_type = 'CST_COST_CODE_TYPE' left join mfg_lookups ml on ml.lookup_code = wdj.job_type and ml.lookup_type = 'WIP_DISCRETE_JOB' 。其中mmt,we,mta,msi,wdj数据量很大

针对这个SQL语句，可以优化的地方有：

1. 使用JOIN语句时，可以根据数据量大小，将数据量大的表放在后面，这样可以避免在连接时出现性能问题。

2. 使用子查询时，可以在子查询中添加条件筛选，减少返回的数据量。

3. 可以对查询中的日期条件进行优化，例如使用日期范围查询时，可以使用BETWEEN关键字代替大于等于和小于等于的运算符。

4. 可以对大表进行分区或分片，以加快查询速度。

5. 可以对JOIN语句中的字段添加索引，以提高查询效率。

下面是对原SQL语句的优化：

SELECT 
    we.organization_id, 
    we.wip_entity_id, 
    CASE WHEN wl.line_id is null THEN we.wip_entity_name ELSE '' END wip_entity_name,
    we.primary_item_id, 
    mtt.transaction_type_name, 
    mmt.transaction_date, 
    bd.department_code, 
    mmt.inventory_item_id, 
    mmt.subinventory_code, 
    mta.reference_account, 
    br.resource_code, 
    lu2.meaning as line_type_name,
    mta.base_transaction_value, 
    mta.cost_element_id, 
    flv.meaning as cost_element, 
    wdj.class_code job_type_code, 
    ml.meaning job_type_name 
FROM 
    gerp.wip_entities we 
    INNER JOIN (
        SELECT 
            * 
        FROM 
            gerp.mtl_material_transactions 
        WHERE 
            transaction_date BETWEEN '2023-06-01' AND '2023-06-30' 
            AND transaction_source_type_id = 5
    ) mmt ON mmt.organization_id = we.organization_id 
    INNER JOIN gerp.mtl_transaction_accounts mta ON mta.transaction_source_id = we.wip_entity_id 
        AND mta.transaction_id = mmt.transaction_id 
        AND mta.transaction_source_type_id = 5 
    INNER JOIN gerp.mtl_transaction_types mtt ON mtt.transaction_type_id = mmt.transaction_type_id 
    INNER JOIN mfg_lookups lu2 ON lu2.lookup_code = mta.accounting_line_type AND lu2.lookup_type = 'CST_ACCOUNTING_LINE_TYPE' 
    INNER JOIN gerp.mtl_system_items_b msi ON msi.inventory_item_id = mmt.inventory_item_id 
        AND msi.organization_id = mta.organization_id 
    LEFT JOIN gerp.bom_departments bd ON bd.department_id = mmt.department_id 
    LEFT JOIN gerp.bom_resources br ON br.resource_id = mta.resource_id 
    LEFT JOIN gerp.wip_lines wl ON wl.line_id = mmt.repetitive_line_id 
    LEFT JOIN gerp.wip_discrete_jobs wdj ON wdj.wip_entity_id = mta.transaction_source_id 
    LEFT JOIN gerp.fnd_lookup_values_vl flv ON cast(mta.cost_element_id as string) = flv.lookup_code 
        AND flv.lookup_type = 'CST_COST_CODE_TYPE' 
    LEFT JOIN mfg_lookups ml ON ml.lookup_code = wdj.job_type AND ml.lookup_type = 'WIP_DISCRETE_JOB';

在优化后的SQL语句中，将子查询中的日期范围查询放在了WHERE语句中，将数据量较大的表放在了后面，左连接的表也放在了后面。同时，可以根据具体情况对需要添加索引的字段进行索引优化。