Examples of how to use dates in Oracle

Catalog

Preface

1 The date is equal to \ Greater than \ Less than

2 Date difference calculation

1 Directly subtract the two times

2 Two level conversion of time and date

3 Use trunc function

summary

Preface

In the use of sql Function time , Due to different project databases , Lead to sql The use of dates in is very different , Some common date calculations , There are different applications , So sort out the records Oracle Date usage of .
With user Table as an example

CREATE TABLE "SCOTT"."user" ("id" NUMBER(20,0) NOT NULL ENABLE, "name" VARCHAR2(30), "age" NUMBER(11,0), "email" VARCHAR2(50), "crt_time" DATE, PRIMARY KEY ("id") USING INDEX PCTFREE 10 INITRANS 2 MAXTRANS 255 NOCOMPRESS LOGGING TABLESPACE "USERS" ENABLE ) SEGMENT CREATION DEFERRED PCTFREE 10 PCTUSED 40 INITRANS 1 MAXTRANS 255 NOCOMPRESS LOGGING TABLESPACE "USERS"-- Add basic data INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('1', 'Jone', '18', '''[email protected]', TO_DATE('2022-04-01 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('2', 'Jone', '20', '''[email protected]', TO_DATE('2022-04-02 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('3', 'Jone', '28', '''[email protected]', TO_DATE('2022-04-03 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('4', 'Jone', '21', '''[email protected]', TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('5', 'Jone', '24', '''[email protected]', TO_DATE('2022-04-05 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));INSERT INTO "SCOTT"."user"("id", "name", "age", "email", "crt_time") VALUES ('6', 'Jone', '12', '''[email protected]', TO_DATE('2022-04-06 22:20:02', 'SYYYY-MM-DD HH24:MI:SS'));1 The date is equal to \ Greater than \ Less than

Oracle The size of the date in , It is usually converted into a string for comparison .

explain :

dual yes oracle An internal table defined in , Only one row and one column

SYSDATE The function represents the current time

to_char(date,‘format’) function , Parameters date For date type , Parameters format Represents the format of the conversion , What is commonly used is 'yyyy-mm-dd hh24:mi:ss' ( Case sensitive )

-- Look at two times select TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS') , SYSDATE FROM dual-- result -- 2022-04-04 22:20:022022-04-10 22:31:43-- A simple case -- 1 Time comparison Because the incoming time is less than the current time Result set is empty select TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS') , SYSDATE FROM dualwhere TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS') > SYSDATE -- Empty string Empty string -- 2 Time comparison Because the incoming time is less than the current time Result set has value select TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS') , SYSDATE FROM dualwhere TO_DATE('2022-04-04 22:20:02', 'SYYYY-MM-DD HH24:MI:SS') < SYSDATE -- 2022-04-04 22:20:022022-04-10 22:37:502 Date difference calculation

demand : Calculate the difference in days between the two times

1 Directly subtract the two times

Subtracting two dates , What you get is data with an accuracy of minutes and seconds , Unqualified

SELECT SYSDATE- to_date('2022-04-10 22:20:02','yyyy-mm-dd hh24:mi:ss')FROM dual-- result 0.01813657407407407407407407407407407407412 Two level conversion of time and date

to_date(string,‘format’) function , Is to convert a string to date Time .

SELECT to_date(to_char(SYSDATE,'yyyy-mm-dd'),'YYYY-MM-DD HH24:MI:SS') - to_date(to_char(to_date( '2022-04-10 22:20:02', 'YYYY-MM-DD HH24:MI:SS' ) ,'yyyy-mm-dd'),'YYYY-MM-DD HH24:MI:SS')FROM dual;-- result : 0

This method is cumbersome , And after many transformations , Low efficiency .

3 Use trunc function

trunc() function .

effect : Used to intercept time or value , Returns the specified value .

Date processing ：

TRUNC(date,[format])

date For the necessary parameters , Is an input date Date value .

format Parameters can be ignored , Specify date format , By default, it indicates the of the specified date 0 spot .

SELECTSYSDATE,to_date( '2022-04-10 22:20:02', 'YYYY-MM-DD HH24:MI:SS' ), trunc(SYSDATE) - trunc(to_date( '2022-04-10 22:20:02', 'YYYY-MM-DD HH24:MI:SS' ))FROM dual;

Besides , This function can also be used for numerical processing .

TRUNC(number,[decimals])

number For the necessary parameters , Is an input number The number .

decimals Parameters can be ignored , Specify the number of bits to intercept , By default, the value after the decimal point is truncated

SELECT3.0,2.22, trunc(3.0) - trunc(2.22,1)FROM dual;-- result 3 2.22 0.8 summary

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