Add Difference Between Explain And Explain Analyze as a postgres til

README.md

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-_861 TILs and counting..._
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 - [Default Schema](postgres/default-schema.md)
 - [Defining Arrays](postgres/defining-arrays.md)
 - [Determining The Age Of Things](postgres/determining-the-age-of-things.md)
+- [Difference Between Explain And Explain Analyze](postgres/difference-between-explain-and-explain-analyze.md)
 - [Dump And Restore A Database](postgres/dump-and-restore-a-database.md)
 - [Edit Existing Functions](postgres/edit-existing-functions.md)
 - [Escaping A Quote In A String](postgres/escaping-a-quote-in-a-string.md)

postgres/difference-between-explain-and-explain-analyze.md

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+# Difference Between Explain And Explain Analyze
+
+The `explain` statement allows you to gain some insight into the performance of
+a query. You may hear `explain` and `explain analyze` referred to
+interchangeably in conversation. Though they can both be used to explore how a
+query will perform, it's important to know a key difference. `explain analyze`
+executes the query, `explain` does not.
+
+For `select` queries, the distinction may not feel that important. For
+`insert`s, `update`s, and `delete`s, you'll want to be clear about which one
+you are using.
+
+```sql
+> explain insert into books (title, author) values ('Fledgling', 'Octavia Butler');
+                     QUERY PLAN
+----------------------------------------------------
+ Insert on books  (cost=0.00..0.01 rows=1 width=76)
+   ->  Result  (cost=0.00..0.01 rows=1 width=76)
+
+> select count(*) from books;
+ count
+-------
+     0
+```
+
+With `explain`, you get cost estimates of the `insert` statement.
+
+```sql
+> explain analyze insert into books (title, author) values ('Fledgling', 'Octavia Butler');
+                                          QUERY PLAN
+----------------------------------------------------------------------------------------------
+ Insert on books  (cost=0.00..0.01 rows=1 width=76) (actual time=0.285..0.285 rows=0 loops=1)
+   ->  Result  (cost=0.00..0.01 rows=1 width=76) (actual time=0.012..0.012 rows=1 loops=1)
+ Planning time: 0.021 ms
+ Execution time: 0.309 ms
+
+> select count(*) from books;
+ count
+-------
+     1
+```
+
+With `explain analyze`, you get estimates and actual numbers. You also get a
+row inserted in the `books` table.