Data update

Task/Conditional-structures/MariaDB/conditional-structures-2.sql

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+SELECT
+    -- return the first non-NULL value
+    COALESCE(email, phone, telegram_id) AS contact,
+    -- replace the key (1) with corresponding value ('email')
+    CASE contact_type WHEN 1 THEN 'email' WHEN 2 THEN 'phone' ELSE NULL END AS contact_type,
+    -- the first parameter must be a 1-based integer,
+    -- ELT() returns the nth argument (eg, for n=1 it will return the email column)
+    ELT(n, email, phone, telegram_id) AS preferred_contact,
+    -- returns the index of the value that is equal to the 1st argument:
+    -- in this example, 2
+    FIELD('phone',  'email', 'phone', 'telegram_id') AS type;
+    FROM user;