测试基础数据库 sql 查询常用高阶方法

周小丽 · 2022年10月17日 · 最后由 disciple 回复于 2022年11月17日 · 5813 次阅读

1、常用时间、日期函数

需要结合 to_date 、to_char 两个函数使用，库表时间类型有的是 varchar 类型的，要转成时间类型

① 获取当前时间：current_timestamp，localtimestamp

② 获取当前日期：CURRENT_date

③ 获取当前月份：to_char(now(),'yyyy-MM')

④ 获取近7天的数据
SELECT * from cm_capital_outflow where to_char(date,'yyyy-mm-dd') BETWEEN to_char( CURRENT_DATE - INTERVAL '7 day', 'yyyy-mm-dd' ) AND to_char( CURRENT_DATE, 'yyyy-mm-dd' )

⑤获取近一个月的数据
 to_char( CURRENT_DATE - INTERVAL '1 months', 'yyyy-mm-dd' )

⑥获取近一年的数据
to_char( CURRENT_DATE - INTERVAL '1 year', 'yyyy-mm-dd' )

⑦毫秒时间戳转日期：to_timestamp(round(start_time/1000))

⑧秒时间戳转日期：to_timestamp(long_)

⑨日期字段截取年份：date_part('year',f_fromdate)

2、With 的用法

With 子句有助于将复杂的查询分解为更简单的语句，便于阅读，也可以当做一个为查询而存在的临时表，WITH 子句在使用前必须先定义.
格式： with 自定义表名 1 as(后面跟着 sql 语句的查询),自定义表名 2 as(后面跟着 sql 语句的查询)
多个临时表的使用

3、递归查询

在 WITH 子句中可以使用自身输出的数据

1.向上递归
with RECURSIVE hr_dept1 as(
SELECT *  from hr_dept where dept_id='489614256'
union
SELECT hr_dept.* from hr_dept,hr_dept1 where hr_dept.dept_id=hr_dept1.parent_id)----递归查询
SELECT dept_id,dept_name,dept_type,parent_id  from hr_dept1
ORDER BY dept_type

1 sql中with hr_dept1 as () 是对一个查询子句做别名，同时数据库会对该子句生成临时表；
2  recursive 是一个函数，他会把查询出来的结果再次代入到查询子句中继续查询
3 最后一句select后跟的字段必须少于等于hr_dept和hr_dept1中字段。

2.向下递归
with RECURSIVE hr_dept1 as(
SELECT *  from hr_dept where dept_id='51597175'
union
SELECT hr_dept.* from hr_dept,hr_dept1 where hr_dept.parent_id=hr_dept1.dept_id)
SELECT dept_id,dept_name,dept_type,parent_id  from hr_dept1
ORDER BY dept_type

4、select 条件中 case then 的用法

格式：case
when then
when then
.......
end

1、计算不同年龄段人数的占比
2、注意between and 是双包含于的关系
3、目前身份证号长度只有15位、18位两种，所以查询固定长度为15、18的证件号码

select b0/(b0+b18+b30+b50+b70)::float as 零到18岁,b18/(b0+b18+b30+b50+b70)::float as 十八到30岁,b30/(b0+b18+b30+b50+b70)::float as 三十到50岁,b50/(b0+b18+b30+b50+b70)::float as 五十到70岁,b70/(b0+b18+b30+b50+b70)::float as 七十岁以上 from ---计算不同年龄段的人数占比
(
with t as (
SELECT (CURRENT_DATE - to_date(substring(zjhm,7,4),'YYYY'))/365 as age,zjhm ---18位新证件号
from cg.qc_jtcy 
where area_id like '41%' and xb in ('男','女') and length(zjhm)=18
GROUP BY zjhm 
union all
SELECT (CURRENT_DATE - to_date('19'||substring(zjhm,7,2),'YYYY'))/365 as age,zjhm ---15位老证件号
from cg.qc_jtcy 
where area_id like '41%' and xb in ('男','女') and length(zjhm)=15
GROUP BY zjhm---t表根据身份证号计算年龄,并通过group by对证件号去重处理
)
select 
count(case when age between 0 and 17 then 1 end) as b0,
count(case when age between 18 and 29 then 1 end) as b18,
count(case when age between 30 and 49 then 1 end) as b30,
count(case when age between 50 and 69 then 1 end) as b50,
count(case when age >70 or age =70 then 1 end) as b70
from t ---b表是根据身份证号计算不同年龄段的人数
)b

5、where 条件中 case when 的用法

select b.qhmc as name,sum(a.tbmj) as datas from yw_tjxxb_cb a
INNER join sys_adminarea b on a.qhdm = b.qhdm
where bxgsdm='6' and nf='2021' and zwdm in('07', '02', '52', '23', '17','04', '22', '53', '03', '06', '16', '01', '08') and 
case when length(rtrim('1000000', '0')) = 1 then length(a.qhdm) = 2
when length(rtrim('100000', '0')) = 2 then length(a.qhdm) = 4 and a.qhdm like concat(rtrim('100000', '0'),'%')
when length(rtrim('100000', '0')) = 4 then length(a.qhdm) = 6 and a.qhdm like concat(rtrim('100000', '0'),'%')
when length(rtrim('100000', '0')) = 6 then length(a.qhdm) = 9 and a.qhdm like concat(rtrim('100000', '0'),'%')
when length(rtrim('100000', '0')) = 9 then length(a.qhdm) = 12 and a.qhdm like concat(rtrim('100000', '0'),'%')
else a.qhdm = rtrim('100000', '0') end
GROUP BY b.qhmc

备注：length(rtrim('6500200', '0')) = 2  去除右侧所有的0后长度为2，
length(a.qhdm) = 4    取qhdm长度为4的区划
a.qhdm like concat(rtrim('650000', '0'),'%')     并且 qhdm是以去除0后的区划开始的
也就是说查出65甘肃省下所有的市（市是4位区划）

BI大屏中’100000’ 需要替换为变量，比如'${qhdm}'

6、case when 给字段赋值

select qhdm,
   (case 
    when substring (bdh,21,12) <> qhdm then 'qhdm错误'
        when substring (bdh,1,4) <> nf then 'nf错误'
        when substring (bdh,7,1) <> datagroup then 'tbj错误'
    end
   )bdh
from yw_tbqdstatus ORDER BY bdh

7、HAVING 配合 GROUP BY 子句，在创建的分组上设置条件

例子：查询一个表中身份证号重复的数据。

SELECT id_card ,count(*) FROM hr_employee
GROUP BY id_card
HAVING count(*) >1

计算查询统计结果中大于阈值的数

select dkbm,sum(cdbl)as cdbl from yw_cbycfxtjb 
where rwid = 'D71C70DA7AAF4726A109EEDCB8F423DC' 
group by dkbm having sum(cdbl) < 0.1 
order by cdbl

8、UNION 和 UNION all 的区别

①UNION 操作符用于合并两个或多个 SELECT 语句的结果集。
②UNION ALL 操作符可以连接两个有重复行的 SELECT 语句。

9、类型转换

① postgresql 整数除整数等于0
select round(448/2298::numeric,2)

② 查询重复记录条数
select f_uri,count(*) as c from tbdm_files group by f_uri order by count(*) desc

③ Nhid解密：select decode_sfzh(nhid)

④ 数字转字符串  select cast(123 as VARCHAR); 
⑤ 字符串转数字  select cast('123' as INTEGER);
⑥ 避免空值转换报错CAST( COALESCE( NULLIF( col, ‘’), ‘0’) AS INTEGER)
⑦ 日期转字符串 to_char(check_date,'yyyy-mm')

10、跨库查询

SELECT code FROM dblink
     (  'dbname=cic_sys user=postgres password=postgresql  host=localhost port=3002',
        'select code from sys_dept where parent_ids like ''%,41,%'' or code = ''41''') t(code character  varying)

11、将纵向数据改成横向数据显示

SELECT dkbm,
sum(case when xsz=1 then xsz else null end) as xsz1,
sum(case when xsz=2 then xsz else null end) as xsz2,
sum(case when xsz=3 then xsz else null end) as xsz3,
sum(case when xsz=4 then xsz else null end) as xsz4,
sum(case when xsz=15 then xsz else null end) as xsz5 
FROM yw_proc_rhgcb_s WHERE qhdm = '411328102200' GROUP BY dkbm;

12、string_agg 同字段内容合并

多个字段相同，一个字段不同，将那个不同字段的字符进行拼接，将多条记录显示为一条记录（其他相同字段 group by）
string_agg(DISTINCT b.animal_type,',')

13、将两个不同的字段进行拼接

SELECT work_end_time|| '-' || work_start_time as 作业时间端

14、字符转数值类型，若空字符串则为 0.00

round(sum(cast(COALESCE(nullif(check_result,''),'0.00') as numeric))/count(distinct sample_code),2)

15、给字段值添加单位

SELECT round(SUM(tbmj)/10000,2) ||'万亩' AS 验标面积 
FROM yw_tjxxb_cb
WHERE qhdm = '41'

16、通过 sql 构建新表

with t as (
  SELECT 
  '[
    {"dm":"1","mc":"种植监测"},
    {"dm":"2","mc":"长势监测"},
    {"dm":"3","mc":"产量监测"},
    {"dm":"4","mc":"灾害监测"}
  ]' as str
)
SELECT 
  replace(cast(json(json_array_elements(cast(str as json))) -> 'dm' AS VARCHAR),'"','') AS dm,
  replace(cast(json(json_array_elements(cast(str as json))) -> 'mc' AS VARCHAR),'"','') AS mc from t;

17、避免科学技术法

select b.qhmc as 区划名称,sum(a.dkje)::decimal::text as 贷款总额 ---避免显示科学计数法

18、取 json 中某个字段的值

SELECT act_hi_procinst.business_key_::json->> 'businessName' as 公文标题

19、从两个无关联的表查数据

SELECT COUNT (A.enterprise_number ),count(b.service_organize_number)
FROM ht_contract A, wp_work_process b

20、两表关联赋值

表 1 与表 2 根据 seriaild 列做关联
修改 set 表 1.receive_ymd=表 2.ymd

UPDATE table_1 
SET receive_ymd=inputymd 
FROM(
    SELECT *
    FROM table_1 AS  ta_1
    INNER JOIN tbale_2 AS tb_2
    ON ta_1.serialid=tb_2.serialid
)tbs
WHERE  table_1.create_time=tbs.create_time AND table_1.serialid=tbs.serialids