SQL - Yash-777/LearnJava GitHub Wiki

Online Fiddles

  • Second Highest salary
-- LIMIT 0 , 30 « Start row: 0, Number of rows: 30 
select DISTINCT salary from Emp order by salary DESC LIMIT 1,1; // 3,1 for 4th highest

select MAX(salary) from Emp where salary NOT IN (select MAX(salary) from Emp)

create table Employee (EmployeeID  int,  Salary int);

insert into Employee values (3, 200);
insert into Employee values (4, 800);
insert into Employee values (7, 450);


SELECT MAX(Salary) FROM Employee 
WHERE Salary < (SELECT MAX(Salary) FROM Employee);

SELECT MAX(Salary) FROM Employee WHERE Salary NOT IN (SELECT MAX(Salary) FROM Employee);

-- MySQL
-- Highest 0,1 Second highest 1,1
SELECT Salary FROM Employee ORDER BY Salary DESC LIMIT 0,1;
SELECT Salary FROM Employee ORDER BY Salary DESC LIMIT 1,1;

-- Limit coun  to return, Offset row start
SELECT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 0;
SELECT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 2;
SELECT * FROM TABLENAME WHERE column in ('val1','val2','val3')
SELECT * FROM TABLENAME WHERE column like '%val1'
  • Update with Select
UPDATE TABLE_NAME,
  ( SELECT MAX(versionColumn) as max from TABLE2 where column='Someval') as outcome
  SET
  columnChange = 'val'
  WHERE
  version = outcome.max and id = 7

A short description of GROUP BY Clause

The GROUP BY clause can be used in a SELECT statement to collect data across multiple records and group the results by one or more columns. The aggregate function columns are not included in GROUP BY cluse, I mean to say the columns that used the aggregate function is not included in the GROUP BY cluse.

The HAVING cluse is used to filters the GROUP BY cluse.

Example:

SELECT columns1, columns2, SUM(columns3)
FROM Mytable
GROUP BY columns1, columns2
HAVING columns1>0
  • SQL CASE Statements is the closest to IF in SQL and is supported on all versions of SQL Server
SELECT CASE <variable> 
            WHEN <value>      THEN <returnvalue>
            WHEN <othervalue> THEN <returnthis>
                              ELSE <returndefaultcase>
       END AS <newcolumnname>
FROM <table>
-- (OR ) To cast for appropriate type
SELECT CAST(CASE <variable> 
            WHEN <value>      THEN <returnvalue>
            WHEN <othervalue> THEN <returnthis>
            ELSE <returndefaultcase>
       END AS columnType) as <newcolumnname>
FROM <table>

Get data form three tables.

Project_Module:

P_ID M_ID
1 2
7 1

Project:

P_ID Name
1 Loing
7 Check Out

Module:

M_ID Name
2 Possitive
1 Negative

Outer Join example

SELECT pm.`M_ID` , p.`NAME` , m.`NAME` 
FROM
`Project_Module` pm
JOIN  `Project`  p   ON ( pm.`P_ID` = p.`P_ID` ) 
JOIN  `Module`   m   ON ( pm.`M_ID` = m.`M_ID` ) 
WHERE pm.`P_ID` = 7

DUMP

SELECT `dom` FROM `objectTable` WHERE `pagename` = 'alstate' and `projectid` = '7' and `addedby` = '7' 
and `version` = (SELECT MAX(`version`) as maxvalue FROM `objectTable` WHERE `pagename` = 'alstate') LIMIT 0, 1


UPDATE `objectTable`, (SELECT `dom` as id FROM `objectTable` WHERE `pagename` = 'alstate' and `projectid` = '7' 
and `addedby` = '7' and `version` = (SELECT MAX(`version`) as maxvalue FROM `objectTable` WHERE `pagename` = 'alstate')
 LIMIT 0, 1) as crosscheck SET `dom` = '12121' WHERE crosscheck.id = '0' AND `pagename` = 'alstate'

UPDATE `objectTable`, 
(SELECT MAX(`version`) as maxvalue FROM `objectTable` WHERE `pagename` = 'alstate') as version ,
(SELECT `dom` as id FROM `objectTable` WHERE `pagename` = 'alstate' and `projectid` = '7' and `addedby` = '7' and 
`version` =  (SELECT MAX(`version`) as maxvalue FROM `objectTable` WHERE `pagename` = 'alstate') ) as crosscheck SET `dom`
 = '12121' WHERE crosscheck.id = '12121' AND `pagename` = 'alstate' AND `version` = version.maxvalue

UPDATE `objectTable`, (SELECT MAX(`version`) as maxvalue FROM `objectTable` WHERE `pagename` = ? ) as version, (SELECT 
`dom` as id FROM `objectTable` WHERE `pagename` = ? and `projectid` = ? and `addedby` = ? and `version` =  (SELECT 
MAX(`version`) as maxvalue FROM `objectrepository_temp` WHERE `pagename` = ?) ) as crosscheck SET `dom` = ? WHERE 
crosscheck.id = '0' AND `pagename` = ? AND `version` = version.maxvalue

SQL Statement using Where clause with multiple values 

 PersonName      SongName    Status 
 Holly           Highland    Complete
 Holly           Mech        Complete 
 Ryan            Highland    Complete

select songName from t where personName in ('Ryan', 'Holly') group by songName having count(distinct personName) = 2

select songName from t where personName in ('Ryan', 'Holly') and status = 'Complete'

How to check RMAN backup status and timings Stackpost

V$RMAN_BACKUP_JOB_DETAILS displays details about backup jobs.

select d.name, to_char(START_TIME,'dd-mon-yyyy hh24:mi:ss') start_time, 
  to_char(END_TIME,'dd-mon-yyyy hh24:mi:ss') end_time, ELAPSED_SECONDS, time_taken_display, INPUT_TYPE 
  from   v$rman_backup_job_details, v$database d
  where  INPUT_TYPE = 'DB INCR'
  order  by to_date(start_time,'dd-mon-yyyy hh24:mi:ss');
  
select d.name, to_char(START_TIME,'dd-mon-yyyy hh24:mi:ss') start_time, 
  to_char(END_TIME,'dd-mon-yyyy hh24:mi:ss') end_time, ELAPSED_SECONDS, time_taken_display, INPUT_TYPE 
  from   v$rman_backup_job_details, v$database d
  where  INPUT_TYPE like '%DB%' 
  order  by to_date(start_time,'dd-mon-yyyy hh24:mi:ss') desc
  FETCH FIRST 1 ROWS ONLY;
  -- OFFSET 1 ROWS FETCH NEXT 1 ROWS ONLY;
  
select d.name from v$database d;
select max(start_time) as max_start_time from v$rman_backup_job_details;
CREATE TABLE YASH_INFO
  (
    "ID"   NUMBER NOT NULL ENABLE,
    "NAME" VARCHAR2(500 BYTE),
    "TEXTFILE" CLOB,
    "BLOBFILE" BLOB,
    "DATEINSERTION" DATE,
    "TIMESTAMPDATE" TIMESTAMP (6),
    "CONTENTTYPE" VARCHAR2(50 BYTE)
  );

SELECT SYSDATE FROM DUAL;
SELECT SYSTIMESTAMP FROM DUAL;

SELECT (SYSDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60 * 1000 FROM DUAL; -- 1584029850000

-- Convert current time to epoch.
select ((cast (systimestamp at time zone 'UTC' as date) - date '1970-01-01') * 86400) as epoch from dual;
-- Convert hard-coded timestamp to epoch.
select ((cast (timestamp '2019-12-31 23:59:59' at time zone 'UTC' as date) - date '1970-01-01') * 86400) as epoch from dual;

SELECT TIMESTAMPDATE, to_char(TIMESTAMPDATE, 'YYYYMMDD') as sot from YASH_INFO order by TIMESTAMPDATE, sot asc;
select ((cast (TIMESTAMPDATE at time zone 'UTC' as date) - date '1970-01-01') * 86400) as epoch from YASH_INFO;

-- ======================
SELECT * from YASH_INFO order by TIMESTAMPDATE asc;
SELECT * from YASH_INFO order by TIMESTAMPDATE, ((cast (TIMESTAMPDATE at time zone 'UTC' as date) - date '1970-01-01') * 86400) asc;

SELECT * from YASH_INFO order by DATEINSERTION asc;
-- ======================

SELECT TIMESTAMPDATE, CONVERT(VARCHAR(6), TIMESTAMPDATE, 112) as sot from YASH_INFO order by TIMESTAMPDATE, sot asc;

select (cast(sys_extract_utc(current_timestamp) as date) - TO_DATE('1970-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS')) * 86400 
  as gmt_epoch from dual;

SELECT TIMESTAMPDATE, ( CAST(FROM_TZ( CAST( TIMESTAMPDATE AS TIMESTAMP ), 'Europe/Berlin'  ) AT TIME ZONE 'UTC'  AS DATE  )*24*60*60) as epoch 
  from YASH_INFO order by TIMESTAMPDATE, epoch asc;

SELECT * from YASH_INFO order by ((TIMESTAMPDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60 * 1000) asc;
 
SELECT (TIMESTAMPDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60 * 1000 as aa from YASH_INFO;
 
SELECT * from YASH_INFO order by (cast(sys_extract_utc(TIMESTAMPDATE) as date) - TO_DATE('1970-01-01 00:00:00','YYYY-MM-DD HH24:MI:SS')) * 86400 asc;

SELECT * from YASH_INFO order by TIMESTAMPDATE, TO_DATE(to_char(TIMESTAMPDATE, 'DD-MON-YYYY'), 'DD-MON-YYYY') asc;
SELECT TIMESTAMPDATE, TO_DATE(to_char(TIMESTAMPDATE, 'DD-MON-YYYY'), 'DD-MON-YYYY') as sot from YASH_INFO order by TIMESTAMPDATE, sot asc;
SELECT * from YASH_INFO order by DATEINSERTION asc;

SELECT * from YASH_INFO ORDER BY cast(DATEINSERTION, datetime) ASC;

SELECT CONVERT(DATEINSERTION, SWITCHOFFSET(CONVERT(datetimeoffset, gETDATE()), DATENAME(TzOffset, gETDATE() 
  AT TIME ZONE 'Eastern Standard Time'))) FROM YASH_INFO order by DATEINSERTION asc;

INSERT INTO "NEON30"."YASH_INFO" (ID, NAME, DATEINSERTION, TIMESTAMPDATE) VALUES ('5', 'test', TO_DATE('12-MAR-20 15.21.43',
   'DD-MON-RR HH24.MI.SS'), TO_TIMESTAMP('08-FEB-20 11.21.49.847000000 PM', 'DD-MON-RR HH.MI.SS.FF AM'))
INSERT INTO "NEON30"."YASH_INFO" (ID, NAME, DATEINSERTION, TIMESTAMPDATE) VALUES ('6', 'test', TO_DATE('12-MAR-20 15.21.43',
   'DD-MON-RR HH24.MI.SS'), TO_TIMESTAMP('08-FEB-20 11.21.49.847000000 AM', 'DD-MON-RR HH.MI.SS.FF AM'))

INSERT INTO "NEON30"."YASH_INFO" (ID, NAME, TEXTFILE, DATEINSERTION, TIMESTAMPDATE, CONTENTTYPE) VALUES ('1', 'test.xml',
   '<xml> </xml>', TO_DATE('07-FEB-20', 'DD-MON-RR'), TO_TIMESTAMP('07-FEB-20 11.01.36.408000000 AM', 'DD-MON-RR HH.MI.SSXFF AM'), 'text/xml')
INSERT INTO "NEON30"."YASH_INFO" (ID, NAME, BLOBFILE, DATEINSERTION, TIMESTAMPDATE, CONTENTTYPE) VALUES ('2', 'jira.xlsx',
   empty_blob(), TO_DATE('07-FEB-20', 'DD-MON-RR'), TO_TIMESTAMP('07-FEB-20 11.04.26.831000000 AM', 'DD-MON-RR HH.MI.SSXFF AM'), 'application/vnd.ms-excel')
SELECT BLOBFILE FROM "NEON30"."YASH_INFO" WHERE ROWID='AAAvD2AAnAAAAQ1AAB' AND ORA_ROWSCN='8662269138106' FOR UPDATE

TO_DATE('07-FEB-20', 'DD-MON-RR'), TO_TIMESTAMP('07-FEB-20 11.01.36.408000000 AM', 'DD-MON-RR HH.MI.SSXFF AM')

UPDATE SET field_name = REPLACE(field_name , 'oldstring', 'newstring') and File Upload from server path.

-- test.xml
update YASH_INFO t 
set t.name = REPLACE(t.name, substr(t.name, instr(t.name,'.xml')), 'Sample.xml')
where ID = 1; -- testSample.xml

-- test_Sample.xml
update YASH_INFO t 
set t.name=replace(t.name, 'Sample', '_Sample')
where ID = 1;

In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behavior.

Method signature: It consists of method name and parameter list (number/type/order of the parameters). methodName(parametersList y). An instance method in a subclass with the same signature and return type as an instance method in the super-class overrides the super-class's method.

Java OOP concepts
Class  - Collection of a common features of a group of object [static/instance Fields, blocks and Methods]
Object - Instance of a class (instance fields)
Abstraction - Process of hiding complex info and providing required info like API, Marker Interfaces ...
Encapsulation(Security) - Class Binding up with data members(fields) and member functions.
Inheritance  (Reusability by placing common code in single class)
 1. Multilevel - {A -> B -> C} 2. Multiple - Diamond problem {A <- (B) -> C} [Java not supports] 3. Cyclic {A <-> B} [Java not supports]
 * Is-A   Relation - Class A extends B
 * Hash-A Relation - Class A { B obj = new B(); } - (Composition/Aggregation)
Polymorphism (Flexibility) 1. Compile-Time Overloading    2. Runtime Overriding  [Greek - "many forms"]


int[] arr = {1,2,3}; int arrLength = arr.length;   // Fixed length of sequential blocks to hold same data type
String str = "Yash"; int strLength = str.length(); // Immutable Object value can't be changed.

List<?> collections = new ArrayList<String>(); int collectionGroupSize = collections.size();
Map<?, ?> mapEntry = new HashMap<String, String>();
Set<?> keySet = mapEntry.keySet(); // Set of Key's
Set<?> entrySet = mapEntry.entrySet(); // Set of Entries [Key, Value]

// Immutable Objects once created they can't be modified. final class Integer/String/Employee
Integer val = Integer.valueOf("100"); String str2 = String.valueOf(100); // Immutable classes
final class Employee { // All Wrapper classes, java.util.UUID, java.io.File ...
    private final String empName; // Field as Final(values can be assigned only once) Only getter functions.
    public Employee(String name) { this.empName = name; }
}

Native Java Code for Hashtable.h, Hashtable.cpp SQL API.

You can check your current JDK and JRE versions on your command prompt respectively,

  • JDK javac -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/p: javac 1.8.0_121
  • JRE java -version [C:\Program Files\Java\jdk1.8.0_121\bin] o/P: java version "1.8.0_102"

JAVA_HOME - Must be set to JDK otherwise maven projects leads to compilation error. [ERROR] No compiler is provided in this environment. Perhaps you are running on a JRE rather than a JDK? C:\Softwares\OpenJDK\, 7-zip

Fatal error compiling: invalid target release: JRE and JDK must be of same version 1.8.0.XXX

Disable TLS 1.0 and 1.1security-libs/javax.net.ssl: TLS 1.0 and 1.1 are versions of the TLS protocol that are no longer considered secure and have been superseded by more secure and modern versions (TLS 1.2 and 1.3).

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