SQLite

Connections opened with the SQLITE_OPEN_SHARED_SCHEMA flag
specified may not modify any database schema except that belonging to the
temp database in anyway. This includes creating or dropping database 
objects, vacuuming the database, or running ANALYZE when the
sqlite_stat\[14\] tables do not exist.

If the schema of a database attached to an
SQLITE_OPEN_SHARED_SCHEMA database handle is corrupt, or if
corruption is encountered while parsing the database schema, then the
database is treated as empty. This usually means that corruption results in
a "no such table: xxx" error instead of a more specific error message.

For SQLITE_OPEN_SHARED_SCHEMA connections, the
SQLITE_DBSTATUS_SCHEMA_USED sqlite3_db_status() verb
distributes the memory used for a shared schema object evenly between all
database connections that share it.

## Implementation Notes

    goto detach_error;
  }
  if( sqlite3BtreeIsInReadTrans(pDb->pBt) || sqlite3BtreeIsInBackup(pDb->pBt) ){
    sqlite3_snprintf(sizeof(zErr),zErr, "database %s is locked", zName);
    goto detach_error;
  }

  sqlite3SchemaDisconnect(db, i, 0);
  sqlite3BtreeClose(pDb->pBt);
  pDb->pBt = 0;
  pDb->pSchema = 0;
  sqlite3CollapseDatabaseArray(db);
  return;

detach_error:

  char **pzErr
){
  int rc = SQLITE_NOMEM;
  schemapool_vtab *pVtab = sqlite3_malloc(sizeof(schemapool_vtab));
  if( pVtab ){
    memset(pVtab, 0, sizeof(schemapool_vtab));
    rc = sqlite3_declare_vtab(db, SCHEMAPOOL_SCHEMA);
    if( rc!=SQLITE_OK ){
      sqlite3_free(pVtab);
      pVtab = 0;
    }
  }
  *ppVtab = (sqlite3_vtab *)pVtab;
  return rc;
}

/*
** Open a new cursor on the schema table.

  PRAGMA writable_schema = 1;
  UPDATE sqlite_master SET sql='CREATE TABLE t3 a,b' WHERE name = 't3';
}

do_test 5.2 { 
  catchsql { SELECT * FROM t1 } db2
} {1 {malformed database schema (t3) - near "a": syntax error}}

do_test 5.3 { 
  catchsql { SELECT nref,nschema FROM schemapool } db2
} {1 {vtable constructor failed: schemapool}}

do_execsql_test 5.4 {
  PRAGMA writable_schema = 1;
  UPDATE sqlite_master SET sql='CREATE TABLE t3(a,b)' WHERE name = 't3';
}

do_test 5.5 { 
  catchsql { SELECT nref,nschema FROM schemapool } db2
} {0 {1 1}}

finish_test

# 2019 February 12
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
#
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix reuse4

foreach {tn sharedschema} {
  1 0  
  2 1  
} {
  reset_db

  do_execsql_test 1.$tn.0 {
    CREATE TABLE x1(a, b);
    CREATE INDEX x1a ON x1(a);
    CREATE INDEX x1b ON x1(b);
    CREATE TABLE x2(a, b);
  }
  db close
  
  do_test 1.$tn.1 {
    for {set i 1} {$i<4} {incr i} {
      forcedelete test.db$i test.db$i-journal test.db$i-wal
      forcecopy test.db test.db$i
    }
  
    sqlite3 db test.db -shared-schema $sharedschema
    for {set i 1} {$i<4} {incr i} {
      execsql " ATTACH 'test.db$i' AS db$i "
    }
  } {}
  
  do_execsql_test 1.$tn.2 {
    WITH s(i) AS ( SELECT 1 UNION ALL SELECT i+1 FROM s WHERE i<10 )
    INSERT INTO x1 SELECT i, i FROM s;
  
    INSERT INTO db3.x2 SELECT * FROM x1;
    INSERT INTO db2.x1 SELECT * FROM db3.x2;
    CREATE TEMP TRIGGER tr1 AFTER INSERT ON db2.x2 BEGIN
      INSERT INTO x1 VALUES(new.a, new.b);
    END;
    INSERT INTO db2.x2 SELECT * FROM x1 WHERE a%2;
    DELETE FROM x1 WHERE a<3;
    INSERT INTO db3.x1 SELECT * FROM db2.x2;
  
    DETACH db3;
    ATTACH 'test.db3' AS db3;
  
    UPDATE db3.x1 SET a=a-10 WHERE b NOT IN (SELECT b FROM db2.x2);
  
    CREATE TEMP TABLE x1(a, b);
    INSERT INTO db2.x2 VALUES(50, 60), (60, 70), (80, 90);
    ALTER TABLE x1 RENAME TO x2;
    ALTER TABLE x2 ADD COLUMN c;
    ALTER TABLE x2 RENAME a TO aaa;
    DELETE FROM x1 WHERE b>8;
    UPDATE db3.x2 SET b=b*10;
  
    BEGIN;
      CREATE TEMP TABLE x5(x);
      INSERT INTO x5 VALUES(1);
    ROLLBACK;
  
    INSERT INTO main.x2 VALUES(123, 456);
  }
  
  integrity_check 1.$tn.3
  
  do_execsql_test 1.$tn.4 {
    SELECT * FROM main.x1; SELECT 'xxx';
    SELECT * FROM main.x2; SELECT 'xxx';
    SELECT * FROM temp.x2; SELECT 'xxx';
  
    SELECT * FROM db1.x1; SELECT 'xxx';
    SELECT * FROM db1.x2; SELECT 'xxx';
    SELECT * FROM db2.x1; SELECT 'xxx';
    SELECT * FROM db2.x2; SELECT 'xxx';
    SELECT * FROM db3.x1; SELECT 'xxx';
    SELECT * FROM db3.x2; SELECT 'xxx';
  } {
    3 3 4 4 5 5 6 6 7 7 8 8 3 3 5 5 7 7 xxx 
    123 456 xxx 
    50 60 {} 60 70 {} 80 90 {} xxx
    xxx
    xxx
    1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 xxx
    1 1 3 3 5 5 7 7 9 9 50 60 60 70 80 90 xxx
    1 1 3 3  5 5 7 7 9 9 xxx 
    1 10 2 20 3 30 4 40 5 50 6 60 7 70 8 80 9 90 10 100 xxx
  }
  
  do_test 1.$tn.5.1 {
    sqlite3 db2 test.db
    db2 eval { CREATE TABLE x3(x) }
  } {}
  do_execsql_test 1.$tn.5.2 {
    SELECT * FROM main.x1; SELECT 'xxx';
    SELECT * FROM main.x2; SELECT 'xxx';
    SELECT * FROM main.x3; SELECT 'xxx';
  } {
    3 3 4 4 5 5 6 6 7 7 8 8 3 3 5 5 7 7 xxx 
    123 456 xxx 
    xxx
  }
}

finish_test