android.database.sqlite.SQLiteException：靠近“UNION”：語法錯誤

Question

我正在為 android 使用 SQLite 數據庫

SQLite 查詢

SELECT t1.id,t1.name, t1.email FROM ((SELECT id,first_name as 
name,email FROM single_general where unique_code='UD') 
UNION ALL (SELECT name,email FROM school where 
unique_code='UD') ) t1

Answer 1

SELECT 語法不允許關於復合查詢的括號。 刪除它們，以便只留下子查詢周圍的括號：

SELECT id, name, email
FROM (SELECT id, first_name AS name, email
      FROM single_general
      WHERE unique_code = 'UD'
      UNION ALL
      SELECT 0, name, email
      FROM school
      WHERE unique_code = 'UD');

Answer 2

聯合中所有查詢的列數必須相同。 'school' 表查詢中沒有 ID 列。 您可以從“學校”獲取 ID 字段嗎？ 嘗試以下代碼為第二個查詢中的 ID 創建一個 0 填充字段：

SELECT t1.id,t1.name, t1.email FROM ((SELECT id,first_name as 
name,email FROM single_general where unique_code='UD') 
UNION ALL (SELECT 0 as id,name,email FROM `school` where 
unique_code='UD') ) t1