android.database.sqlite.SQLiteException：靠近“UNION”：语法错误

Question

I am using SQLite database for android

SQLite query

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

The SELECT syntax does not allow parentheses about the compound queries. Remove them, so that only the parentheses around the subquery are left:

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

The number of columns in all of queries in the union must be the same. There is no ID column in the 'school' table query. Can you get an ID field from 'school'?. Try the following code creates a 0 filled field for ID in the second query:

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