All language subtitles for 11. Union

Next, we are going to discuss the union operator.
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Union operator combines the result sets of two or more select statement.
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So in except we saw that it is giving us the ResultSet of one table, and from that it removed
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the result set of other table. union is combining both of these ResultSet and while combining
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the duplicate rows from both, the result sets will be removed.
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So it will be similar to the select distinct.
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So the syntax for this union operators, you select the expressions that you want from table one, you
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can specify where conditions also.
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Then you write union, just like we wrote, except then you specify the second select condition with expressions.
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One thing to note here is for expression 1 in the first statement and expression 1 in the second
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statement.
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These two should have the same data types if expression, one in first selected statement is integer then it should be
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integer
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in the second select statement also and the number of expressions in the first select statement, if it is n
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here, it should be.
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n in the second select statement also. you can specify more than two select statements using multiple
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unions.
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Let us look at an example.
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Suppose you want to find out all the customer ideas that you have in your database, either they are
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present in the sales table or they are present in the customer table.
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To do that, to get that combined customer ID table, we will use the union operator will write select customer
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Id from sales table.
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And Union select customer id from customer table, and we will order this by the customer id.
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Let's go right this so select customer id from sales table
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union select customer id from customer table
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order by customer Id.
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Just compare that this is exactly same as the except query that we wrote just that except it replaced
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by Union. Let us run this query
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You can see 10315, which is not president in the customer table is present in our ResultSet,
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10375 is part of both.
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And it is President in the ResultSet, 10480 which is not part of sales table, is present in this result set
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So basically, all the customer ids are present in our result set. This is how we use union and this completes the
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joins and other table combination operators.