Table of Contents
- 1 How do I join two tables with common column in SQL?
- 2 How can I get values for the same column name from two different tables in SQL?
- 3 How can I merge two tables in SQL query?
- 4 Are subqueries inefficient?
- 5 How do you avoid subqueries?
- 6 Can we replace join with subquery?
- 7 Why use subqueries instead of joins?
- 8 Which clauses are not allowed in single row subquery?
- 9 Where Subqueries can not be used?
- 10 Which clause is similar to having clause in SQL?
- 11 Can you have multiple where clauses in SQL?
How do I join two tables with common column in SQL?
The simplest Join is INNER JOIN. INNER JOIN: The INNER JOIN keyword selects all rows from both the tables as long as the condition satisfies. This keyword will create the result-set by combining all rows from both the tables where the condition satisfies i.e value of the common field will be same.
How can I get common data from two tables in SQL?
- Use INNER JOIN with DISTINCT SELECT DISTINCT Table1.colA, Table1.colB, Table1.colC FROM Table1 INNER JOIN Table2 ON Table1.colC = Table2.colZ.
- Use EXISTS SELECT Table1.colA, Table1.colB, Table1.colC FROM Table1 WHERE EXISTS (SELECT 1 FROM Table2 WHERE ColZ = ColC)
How can I get values for the same column name from two different tables in SQL?
If two columns refer to the same thing (like a foreign key and a primary key), make sure they are the same data type. If two columns refer to different things, then give them distinct names. (Do not resort to prefixing every column name with the table name.
How do I join two tables when there is no common column in SQL?
- SELECT column1, column2, etc FROM table1 UNION SELECT column1, column2, etc FROM table2.
- SELECT table1.Column1, table2.Column1 FROM table1 CROSS JOIN table2 WHERE table.Column1 = ‘Some value’
- SELECT table1.Column1, table2.Column2 FROM table1 INNER JOIN table2 ON 1 = 1.
How can I merge two tables in SQL query?
Different Types of SQL JOINs
- (INNER) JOIN : Returns records that have matching values in both tables.
- LEFT (OUTER) JOIN : Returns all records from the left table, and the matched records from the right table.
- RIGHT (OUTER) JOIN : Returns all records from the right table, and the matched records from the left table.
Can we join two tables without condition?
Yes, it is possible to join two tables without using the join keyword. Cross join is also known as cartesian join. If we specify the WHERE condition to the join which we just have seen, we can also convert the same cross join to inner join as well.
Are subqueries inefficient?
Subqueries can be very inefficient. If there are more direct means to achieve the same result, such as using an inner join, you’re better for it. You can nest subqueries up to thirty two levels deep on SQL server.
Should subqueries be avoided?
If you can avoid a subquery and replace it with a JOIN clause, you should do so without hesitation. But of course, in some cases, using a subquery is the only way to solve a data question.
How do you avoid subqueries?
Change the EXISTS statement to a JOIN statement to avoid nested subqueries and reduce the execution time from 1.93 seconds to 1 millisecond. Consider the new execution plan below.
Are subqueries bad SQL?
No, the presence of subqueries does not necessarily mean a database schema is poorly designed. Correlated subqueries should be used sparingly (i.e. when an inner condition refers to an outer clause). Other than that, subqueries are often a useful and a natural way of solving a problem.
Can we replace join with subquery?
A join returns a result table constructed from data from multiple tables. You can also retrieve the same result table using a subquery. A subquery is simply a SELECT statement within another select statement.
Can we use subquery in joins?
A subquery can be used with JOIN operation. The temporary table from the subquery is given an alias so that we can refer to it in the outer select statement. Note that the left and right table of the join keyword must both return a common key that can be used for the join.
Why use subqueries instead of joins?
Subqueries can be used to return either a scalar (single) value or a row set; whereas, joins are used to return rows. A common use for a subquery may be to calculate a summary value for use in a query. For instance we can use a subquery to help us obtain all products have a greater than average product price.
Which clauses can use a subquery?
You can place the Subquery in a number of SQL clauses: WHERE clause, HAVING clause, FROM clause. Subqueries can be used with SELECT, UPDATE, INSERT, DELETE statements along with expression operator. It could be equality operator or comparison operator such as =, >, =, <= and Like operator.
Which clauses are not allowed in single row subquery?
You cannot include text, unitext, or image datatypes in subqueries. Subqueries cannot manipulate their results internally, that is, a subquery cannot include the order by clause, the compute clause, or the into keyword.
How do you use subquery between clauses?
A subquery cannot be immediately enclosed in a set function. The BETWEEN operator cannot be used with a subquery. However, the BETWEEN operator can be used within the subquery.
Where Subqueries can not be used?
4. Where subqueries can not be used? Explanation: The WHERE clause only in the SELECT statement.
How can I use one query result in another?
Use the results of a query as a field in another query. You can use a subquery as a field alias. Use a subquery as a field alias when you want to use the subquery results as a field in your main query. Note: A subquery that you use as a field alias cannot return more than one field.
Which clause is similar to having clause in SQL?
2. Which clause is similar to “HAVING” clause in Mysql? Explanation: “WHERE” is also used to filter the row values in Mysql.
Can we use where and having together in SQL?
A query can contain both a WHERE clause and a HAVING clause. Only the rows that meet the conditions in the WHERE clause are grouped. The HAVING clause is then applied to the rows in the result set.
Can you have multiple where clauses in SQL?
You can specify multiple conditions in a single WHERE clause to, say, retrieve rows based on the values in multiple columns. You can use the AND and OR operators to combine two or more conditions into a compound condition. AND, OR, and a third operator, NOT, are logical operators.
Which clause is used to sort?
An ‘ORDER BY’ clause specifies the sort order. The data is sorted in ascending order by default. To sort in descending order, the keyword DESC is appended to the ‘ORDER BY’ clause.