What is drop database?

What is drop database?

Dropping a database deletes the database from an instance of SQL Server and deletes the physical disk files used by the database. If the database or any one of its files is offline when it is dropped, the disk files are not deleted. These files can be deleted manually by using Windows Explorer.

How do I drop a database in SQL?

To do delete a database you need the command 'DROP DATABASE'. The syntax is similar to creating a database. 'DROP DATABASE ;', where is the name of the database you want to delete.

How do I drop a database in use?

In SQL Server Management Studio 2016, perform the following:

  1. Right click on database.
  2. Click delete.
  3. Check close existing connections.
  4. Perform delete operation.

What is drop SQL?

A DROP statement in SQL removes a component from a relational database management system (RDBMS). ... Unlike TRUNCATE which only deletes the data of the tables, the DROP command deletes the data of the table as well as removes the entire schema/structure of the table from the database.

What is difference between drop and delete in SQL?

DELETE is a Data Manipulation Language command, DML command and is used to remove tuples/records from a relation/table. Whereas DROP is a Data Definition Language, DDL command and is used to remove named elements of schema like relations/table, constraints or entire schema. ... DROP is DDL.

How do I drop a row in SQL?

To remove one or more rows in a table:

  1. First, you specify the table name where you want to remove data in the DELETE FROM clause.
  2. Second, you put a condition in the WHERE clause to specify which rows to remove. If you omit the WHERE clause, the statement will remove all rows in the table.

How do I remove a null row in SQL query?

Use the delete command to delete blank rows in MySQL. delete from yourTableName where yourColumnName=' ' OR yourColumnName IS NULL; The above syntax will delete blank rows as well as NULL row.

Which SQL keyword is used to retrieve a maximum value?

MAX

How do you delete duplicate rows in SQL?

To delete the duplicate rows from the table in SQL Server, you follow these steps:

  1. Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
  2. Use DELETE statement to remove the duplicate rows.

How do you eliminate duplicate rows in SQL query without distinct?

Below are alternate solutions :

  1. Remove Duplicates Using Row_Number. WITH CTE (Col1, Col2, Col3, DuplicateCount) AS ( SELECT Col1, Col2, Col3, ROW_NUMBER() OVER(PARTITION BY Col1, Col2, Col3 ORDER BY Col1) AS DuplicateCount FROM MyTable ) SELECT * from CTE Where DuplicateCount = 1.
  2. Remove Duplicates using group By.

Does inner join return duplicate rows?

Summary. Inner Join can for sure return more records than the records of the table. Inner join returns the results based on the condition specified in the JOIN condition. If there are more rows that satisfy the condition (as seen in query 2), it will return you more results.

How can I delete duplicate rows?

Follow these steps:

  1. Select the range of cells, or ensure that the active cell is in a table.
  2. On the Data tab, click Remove Duplicates (in the Data Tools group).
  3. Do one or more of the following: ...
  4. Click OK, and a message will appear to indicate how many duplicate values were removed, or how many unique values remain.

How can we delete duplicate rows in Oracle without using Rowid?

5 ways to delete duplicate records Oracle

  1. Using rowid. SQL > delete from emp. where rowid not in. (select max(rowid) from emp group by empno); ...
  2. Using self-join. SQL > delete from emp e1. where rowid not in. (select max(rowid) from emp e2. ...
  3. Using row_number() SQL > delete from emp where rowid in. ( ...
  4. Using dense_rank() SQL > delete from emp where rowid in. ( ...
  5. Using group by.

How prevent duplicate rows in SQL JOIN?

The GROUP BY clause at the end ensures only a single row is returned for each unique combination of columns in the GROUP BY clause. This should prevent duplicate rows being displayed in your results.

How do I select without duplicates in SQL?

SQL SELECT DISTINCT Statement SELECT DISTINCT returns only distinct (i.e. different) values. The DISTINCT keyword eliminates duplicate records from the results. DISTINCT can be used with aggregates: COUNT, AVG, MAX, etc. It operates on a single column.

How do I select duplicate rows in SQL?

To select duplicate values, you need to create groups of rows with the same values and then select the groups with counts greater than one. You can achieve that by using GROUP BY and a HAVING clause.

What is difference between unique and distinct?

Unique was the old syntax while Distinct is the new syntax,which is now the Standard sql. Unique creates a constraint that all values to be inserted must be different from the others. Distinct results in the removal of the duplicate rows while retrieving data.

How do I select a single record for duplicates in SQL?

First thing to observe here is that there is no unique column in the table. So we need something to uniquely identify the column in the duplicated table. For this, we can use the ROW_NUMBER() function of SQL server. ROW_NUMBER() returns a unique row number for the current row.

How do I find duplicate keys in SQL?

How to Find Duplicate Values in SQL

  1. Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on.
  2. Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.

Where do I put distinct in SQL?

The SQL DISTINCT keyword is used in conjunction with the SELECT statement to eliminate all the duplicate records and fetching only unique records. There may be a situation when you have multiple duplicate records in a table.

How do I get a single value in SQL?

Introduction to SQL Server SELECT DISTINCT clause The query uses the combination of values in all specified columns in the SELECT list to evaluate the uniqueness. If you apply the DISTINCT clause to a column that has NULL, the DISTINCT clause will keep only one NULL and eliminates the other.

How do I get the last row in SQL?

to get the last row of a SQL-Database use this sql string: SELECT * FROM TableName WHERE id=(SELECT max(id) FROM TableName); Output: Last Line of your db!

IS NULL check in SQL?

The IS NULL condition is used in SQL to test for a NULL value. It returns TRUE if a NULL value is found, otherwise it returns FALSE. It can be used in a SELECT, INSERT, UPDATE, or DELETE statement.

How do I get first or default in SQL?

The FirstOrDefault() method returns a first specific element of a sequence or default value if that element is not found in the sequence. Whenever FirstOrDefault is used, the query can return any amount of results but you state that you only want the first one.

What does SQL return if nothing is found?

If the inner query has a matching row, then 1 is returned. ... If the inner query has no matching row, then it doesn't return anything. The outer query treats this like a NULL, and so the ISNULL ends up returning 0.

What does Rownum do in SQL?

For each row returned by a query, the ROWNUM pseudocolumn returns a number indicating the order in which Oracle selects the row from a table or set of joined rows. The first row selected has a ROWNUM of 1, the second has 2, and so on.

What is difference between FirstOrDefault and SingleOrDefault?

Semantical Difference: FirstOrDefault returns a first item of potentially multiple (or default if none exists). SingleOrDefault assumes that there is a single item and returns it (or default if none exists). Multiple items are a violation of contract, an exception is thrown.

Which is faster SingleOrDefault or FirstOrDefault?

FirstOrDefault is signicantly faster than SingleOrDefault while viewing ANTS profiler. ... Today I used Red Gate ANTS profiler to look into the code and found out my SingleOrDefault call has 18 millions hit for 5000 iterations with (~3.

Which is faster IEnumerable or IQueryable?

A IEnumerable is an "answer", it only has data connected to it but you can't tell what generated that data. ... That is why IQueryable is considered faster, because there is a lot less data that needs to be processed because you where able to ask a more specific question to the server.

Should I use IQueryable or IEnumerable?

IEnumerable: IEnumerable is best suitable for working with in-memory collection (or local queries). IEnumerable doesn't move between items, it is forward only collection. IQueryable: IQueryable best suits for remote data source, like a database or web service (or remote queries).