How-to-obtain-free-records.md (#352)

* How-to-obtain-free-records.md

* Including article in the sidebar

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+# How to obtain free records
+
+On some occasions, we need to obtain or know records whose values are not being occupied.
+
+Either because we want to insert a new value, or we want to restructure our table after a while.
+
+To do this, you can use the following script
+
+```sql
+SELECT t.id +1
+FROM Table1 t
+WHERE NOT EXISTS (
+    SELECT * 
+    FROM Table1 t2
+    WHERE t2.id = t.id + 1
+)
+LIMIT 1
+```
+
+We must replace the name of the table, and the attributes we are looking for.
+
+Now let's look at an example. Let's suppose that we want to search the first free record within `creature`
+
+The first thing we have to identify is your primary key: `guid`
+
+```sql
+SELECT t.`guid` +1
+FROM `creature` t
+WHERE NOT EXISTS (
+    SELECT * 
+    FROM `creature` t2
+    WHERE t2.`guid` = t.`guid` + 1
+)
+LIMIT 1
+```
+
+When running the query, we will get as a result in this case, the number **15**.
+
+What we must do now is to check that this value is not being used, by means of a `SELECT`
+
+```sql
+SELECT * FROM `creature` WHERE `guid`=15;
+```
+
+To corroborate that the information is correct, I leave you the first 16 records.
+
+| guid | id    | map | zoneId |
+|------|-------|-----|--------|
+| 1    | 2843  | 0   | 0      |
+| 2    | 7853  | 0   | 0      |
+| 3    | 2499  | 0   | 0      |
+| 4    | 2838  | 0   | 0      |
+| 5    | 2839  | 0   | 0      |
+| 6    | 2626  | 0   | 0      |
+| 7    | 2482  | 0   | 0      |
+| 8    | 8123  | 0   | 0      |
+| 9    | 9459  | 0   | 0      |
+| 10   | 9520  | 0   | 0      |
+| 11   | 1215  | 0   | 0      |
+| 12   | 1218  | 0   | 0      |
+| 13   | 30140 | 571 | 0      |
+| 14   | 30156 | 571 | 0      |
+| 16   | 32442 | 571 | 0      |
+
+As you can see, number 15 is available.
+
+**Note:** the table has many more attributes, but we show only some, so that the table would not be so extensive.