mysql - 在 MySQL 中使用 IF 语句

Question

我有下面的 SQL 语句。我想要做的是包括一个 IF 语句来涵盖其中一列返回 0 或空白结果的可能性，没有 0 ID。在这种情况下，我试图涵盖 magez_cfv_nations 结果可能返回零或空白结果的可能性。

SELECT c.clan_name, n.nation_name, 
    CONCAT(r.rarity_shorthand, " - ", r.rarity_name) AS rarity_text, 
    t.trigger_name, s.skill_name
 FROM `magez_cfv_cards` AS cards
 JOIN `magez_cfv_clans` c ON cards.clan_id = c.clan_id
 JOIN `magez_cfv_nations` n ON cards.nation_id = n.nation_id
 JOIN `magez_cfv_rarity` r ON cards.rarity_id = r.rarity_id
 JOIN `magez_cfv_trigger` t ON cards.trigger_id = t.trigger_id
 JOIN `magez_cfv_skills` s ON cards.skill_id = s.skill_id

Answer 1

你需要一个 LEFT JOIN

The LEFT JOIN keyword returns all rows from the left table (table_name1), even if there are no matches in the right table

试试这个

SELECT c.clan_name, n.nation_name, 
    CONCAT(r.rarity_shorthand, " - ", r.rarity_name) AS rarity_text, 
    t.trigger_name, s.skill_name
 FROM `magez_cfv_cards` AS cards
 JOIN `magez_cfv_clans` c ON cards.clan_id = c.clan_id
 LEFT JOIN `magez_cfv_nations` n ON cards.nation_id = n.nation_id
 JOIN `magez_cfv_rarity` r ON cards.rarity_id = r.rarity_id
 JOIN `magez_cfv_trigger` t ON cards.trigger_id = t.trigger_id
 JOIN `magez_cfv_skills` s ON cards.skill_id = s.skill_id