SQLite

  ".indexes ?TABLE?       Show names of all indexes\n"
  "                         If TABLE specified, only show indexes for tables\n"
  "                         matching LIKE pattern TABLE.\n"
#ifdef SQLITE_ENABLE_IOTRACE
  ".iotrace FILE          Enable I/O diagnostic logging to FILE\n"
#endif
  ".limit ?LIMIT? ?VAL?   Display or change the value of an SQLITE_LIMIT\n"
  ".lint OPTIONS          Report potential schema issues. Options:\n"
  "                         fkey-indexes     Find missing foreign key indexes\n"
#ifndef SQLITE_OMIT_LOAD_EXTENSION
  ".load FILE ?ENTRY?     Load an extension library\n"
#endif
  ".log FILE|off          Turn logging on or off.  FILE can be stderr/stdout\n"
  ".mode MODE ?TABLE?     Set output mode where MODE is one of:\n"
  "                         ascii    Columns/rows delimited by 0x1F and 0x1E\n"
  "                         csv      Comma-separated values\n"

  rc = _wunlink(z);
  sqlite3_free(z);
#else
  rc = unlink(zFilename);
#endif
  return rc;
}


/*
** The implementation of SQL scalar function fkey_collate_clause(), used
** by the ".lint fkey-indexes" command. This scalar function is always
** called with four arguments - the parent table name, the parent column name,
** the child table name and the child column name.
**
**   fkey_collate_clause('parent-tab', 'parent-col', 'child-tab', 'child-col')
**
** If either of the named tables or columns do not exist, this function
** returns an empty string. An empty string is also returned if both tables 
** and columns exist but have the same default collation sequence. Or,
** if both exist but the default collation sequences are different, this
** function returns the string " COLLATE <parent-collation>", where
** <parent-collation> is the default collation sequence of the parent column.
*/
static void shellFkeyCollateClause(
  sqlite3_context *pCtx, 
  int nVal, 
  sqlite3_value **apVal
){
  sqlite3 *db = sqlite3_context_db_handle(pCtx);
  const char *zParent;
  const char *zParentCol;
  const char *zParentSeq;
  const char *zChild;
  const char *zChildCol;
  const char *zChildSeq;
  int rc;
  
  assert( nVal==4 );
  zParent = (const char*)sqlite3_value_text(apVal[0]);
  zParentCol = (const char*)sqlite3_value_text(apVal[1]);
  zChild = (const char*)sqlite3_value_text(apVal[2]);
  zChildCol = (const char*)sqlite3_value_text(apVal[3]);

  sqlite3_result_text(pCtx, "", -1, SQLITE_STATIC);
  rc = sqlite3_table_column_metadata(
      db, "main", zParent, zParentCol, 0, &zParentSeq, 0, 0, 0
  );
  if( rc==SQLITE_OK ){
    rc = sqlite3_table_column_metadata(
        db, "main", zChild, zChildCol, 0, &zChildSeq, 0, 0, 0
    );
  }

  if( rc==SQLITE_OK && sqlite3_stricmp(zParentSeq, zChildSeq) ){
    char *z = sqlite3_mprintf(" COLLATE %s", zParentSeq);
    sqlite3_result_text(pCtx, z, -1, SQLITE_TRANSIENT);
    sqlite3_free(z);
  }
}


/*
** The implementation of dot-command ".lint fkey-indexes".
*/
static int lintFkeyIndexes(
  ShellState *pState,             /* Current shell tool state */
  char **azArg,                   /* Array of arguments passed to dot command */
  int nArg                        /* Number of entries in azArg[] */
){
  sqlite3 *db = pState->db;       /* Database handle to query "main" db of */
  FILE *out = pState->out;        /* Stream to write non-error output to */
  int bVerbose = 0;               /* If -verbose is present */
  int bGroupByParent = 0;         /* If -groupbyparent is present */
  int i;                          /* To iterate through azArg[] */
  const char *zIndent = "";       /* How much to indent CREATE INDEX by */
  int rc;                         /* Return code */
  sqlite3_stmt *pSql = 0;         /* Compiled version of SQL statement below */

  /*
  ** This SELECT statement returns one row for each foreign key constraint
  ** in the schema of the main database. The column values are:
  **
  ** 0. The text of an SQL statement similar to:
  **
  **      "EXPLAIN QUERY PLAN SELECT rowid FROM child_table WHERE child_key=?"
  **
  **    This is the same SELECT that the foreign keys implementation needs
  **    to run internally on child tables. If there is an index that can
  **    be used to optimize this query, then it can also be used by the FK
  **    implementation to optimize DELETE or UPDATE statements on the parent
  **    table.
  **
  ** 1. A GLOB pattern suitable for sqlite3_strglob(). If the plan output by
  **    the EXPLAIN QUERY PLAN command matches this pattern, then the schema
  **    contains an index that can be used to optimize the query.
  **
  ** 2. Human readable text that describes the child table and columns. e.g.
  **
  **       "child_table(child_key1, child_key2)"
  **
  ** 3. Human readable text that describes the parent table and columns. e.g.
  **
  **       "parent_table(parent_key1, parent_key2)"
  **
  ** 4. A full CREATE INDEX statement for an index that could be used to
  **    optimize DELETE or UPDATE statements on the parent table. e.g.
  **
  **       "CREATE INDEX child_table_child_key ON child_table(child_key)"
  **
  ** 5. The name of the parent table.
  **
  ** These six values are used by the C logic below to generate the report.
  */
  const char *zSql =
  "SELECT "
    "     'EXPLAIN QUERY PLAN SELECT rowid FROM ' || quote(s.name) || ' WHERE '"
    "  || group_concat(quote(s.name) || '.' || quote(f.[from]) || '=?' "
    "  || fkey_collate_clause(f.[table], f.[to], s.name, f.[from]),' AND ')"
    ", "
    "     'SEARCH TABLE ' || s.name || ' USING COVERING INDEX*('"
    "  || group_concat('*=?', ' AND ') || ')'"
    ", "
    "     s.name  || '(' || group_concat(f.[from],  ', ') || ')'"
    ", "
    "     f.[table] || '(' || group_concat(COALESCE(f.[to], "
    "       (SELECT name FROM pragma_table_info(f.[table]) WHERE pk=seq+1)"
    "     )) || ')'"
    ", "
    "     'CREATE INDEX ' || quote(s.name ||'_'|| group_concat(f.[from], '_'))"
    "  || ' ON ' || quote(s.name) || '('"
    "  || group_concat(quote(f.[from]) ||"
    "        fkey_collate_clause(f.[table], f.[to], s.name, f.[from]), ', ')"
    "  || ');'"
    ", "
    "     f.[table] "

    "FROM sqlite_master AS s, pragma_foreign_key_list(s.name) AS f "
    "GROUP BY s.name, f.id "
    "ORDER BY (CASE WHEN ? THEN f.[table] ELSE s.name END)"
  ;

  for(i=2; i<nArg; i++){
    int n = strlen(azArg[i]);
    if( n>1 && sqlite3_strnicmp("-verbose", azArg[i], n)==0 ){
      bVerbose = 1;
    }
    else if( n>1 && sqlite3_strnicmp("-groupbyparent", azArg[i], n)==0 ){
      bGroupByParent = 1;
      zIndent = "    ";
    }
    else{
      raw_printf(stderr, "Usage: %s %s ?-verbose? ?-groupbyparent?\n",
          azArg[0], azArg[1]
      );
      return SQLITE_ERROR;
    }
  }
  
  /* Register the fkey_collate_clause() SQL function */
  rc = sqlite3_create_function(db, "fkey_collate_clause", 4, SQLITE_UTF8,
      0, shellFkeyCollateClause, 0, 0
  );


  if( rc==SQLITE_OK ){
    rc = sqlite3_prepare_v2(db, zSql, -1, &pSql, 0);
  }
  if( rc==SQLITE_OK ){
    sqlite3_bind_int(pSql, 1, bGroupByParent);
  }

  if( rc==SQLITE_OK ){
    int rc2;
    char *zPrev = 0;
    while( SQLITE_ROW==sqlite3_step(pSql) ){
      int res = -1;
      sqlite3_stmt *pExplain = 0;
      const char *zEQP = (const char*)sqlite3_column_text(pSql, 0);
      const char *zGlob = (const char*)sqlite3_column_text(pSql, 1);
      const char *zFrom = (const char*)sqlite3_column_text(pSql, 2);
      const char *zTarget = (const char*)sqlite3_column_text(pSql, 3);
      const char *zCI = (const char*)sqlite3_column_text(pSql, 4);
      const char *zParent = (const char*)sqlite3_column_text(pSql, 5);

      rc = sqlite3_prepare_v2(db, zEQP, -1, &pExplain, 0);
      if( rc!=SQLITE_OK ) break;
      if( SQLITE_ROW==sqlite3_step(pExplain) ){
        const char *zPlan = (const char*)sqlite3_column_text(pExplain, 3);
        res = (0==sqlite3_strglob(zGlob, zPlan));
      }
      rc = sqlite3_finalize(pExplain);
      if( rc!=SQLITE_OK ) break;

      if( res<0 ){
        raw_printf(stderr, "Error: internal error");
        break;
      }else{
        if( bGroupByParent 
        && (bVerbose || res==0)
        && (zPrev==0 || sqlite3_stricmp(zParent, zPrev)) 
        ){
          raw_printf(out, "-- Parent table %s\n", zParent);
          sqlite3_free(zPrev);
          zPrev = sqlite3_mprintf("%s", zParent);
        }

        if( res==0 ){
          raw_printf(out, "%s%s --> %s\n", zIndent, zCI, zTarget);
        }else if( bVerbose ){
          raw_printf(out, "%s/* no extra indexes required for %s -> %s */\n", 
              zIndent, zFrom, zTarget
          );
        }
      }
    }
    sqlite3_free(zPrev);

    if( rc!=SQLITE_OK ){
      raw_printf(stderr, "%s\n", sqlite3_errmsg(db));
    }

    rc2 = sqlite3_finalize(pSql);
    if( rc==SQLITE_OK && rc2!=SQLITE_OK ){
      rc = rc2;
      raw_printf(stderr, "%s\n", sqlite3_errmsg(db));
    }
  }else{
    raw_printf(stderr, "%s\n", sqlite3_errmsg(db));
  }

  return rc;
}

/*
** Implementation of ".lint" dot command.
*/
static int lintDotCommand(
  ShellState *pState,             /* Current shell tool state */
  char **azArg,                   /* Array of arguments passed to dot command */
  int nArg                        /* Number of entries in azArg[] */
){
  int n;
  n = (nArg>=2 ? strlen(azArg[1]) : 0);
  if( n<1 || sqlite3_strnicmp(azArg[1], "fkey-indexes", n) ) goto usage;
  return lintFkeyIndexes(pState, azArg, nArg);

 usage:
  raw_printf(stderr, "Usage %s sub-command ?switches...?\n", azArg[0]);
  raw_printf(stderr, "Where sub-commands are:\n");
  raw_printf(stderr, "    fkey-indexes\n");
  return SQLITE_ERROR;
}


/*
** If an input line begins with "." then invoke this routine to
** process that line.
**
** Return 1 on error, 2 to exit, and 0 otherwise.
*/

        sqlite3_limit(p->db, aLimit[iLimit].limitCode,
                      (int)integerValue(azArg[2]));
      }
      printf("%20s %d\n", aLimit[iLimit].zLimitName,
             sqlite3_limit(p->db, aLimit[iLimit].limitCode, -1));
    }
  }else

  if( c=='l' && n>2 && strncmp(azArg[0], "lint", n)==0 ){
    open_db(p, 0);
    lintDotCommand(p, azArg, nArg);
  }else

#ifndef SQLITE_OMIT_LOAD_EXTENSION
  if( c=='l' && strncmp(azArg[0], "load", n)==0 ){
    const char *zFile, *zProc;
    char *zErrMsg = 0;
    if( nArg<2 ){
      raw_printf(stderr, "Usage: .load FILE ?ENTRYPOINT?\n");

# 2016 December 15
#
# 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 shell6
set CLI [test_find_cli]
db close
forcedelete test.db test.db-journal test.db-wal

foreach {tn schema output} {
  1 {
    CREATE TABLE p1(a PRIMARY KEY, b);
    CREATE TABLE c1(x, y REFERENCES p1);
  } {
    CREATE INDEX 'c1_y' ON 'c1'('y'); --> p1(a)
  }

  2 {
    CREATE TABLE p1(a PRIMARY KEY, b);
    CREATE TABLE c2(x REFERENCES p1, y REFERENCES p1);
  } {
    CREATE INDEX 'c2_y' ON 'c2'('y'); --> p1(a)
    CREATE INDEX 'c2_x' ON 'c2'('x'); --> p1(a)
  }

  3 {
    CREATE TABLE 'p 1'(a, b, c, PRIMARY KEY(c, b));
    CREATE TABLE 'c 1'(x, y, z, FOREIGN KEY (z, y) REFERENCES 'p 1');
  } {
    CREATE INDEX 'c 1_z_y' ON 'c 1'('z', 'y'); --> p 1(c,b)
  }

  4 {
    CREATE TABLE p1(a, 'b b b' PRIMARY KEY);
    CREATE TABLE c1('x y z' REFERENCES p1);
    CREATE INDEX i1 ON c1('x y z') WHERE "x y z" IS NOT NULL;
  } {
  }

  5 {
    CREATE TABLE p1(a, 'b b b' PRIMARY KEY);
    CREATE TABLE c1('x y z' REFERENCES p1);
    CREATE INDEX i1 ON c1('x y z') WHERE "x y z" IS NOT 12;
  } {
    CREATE INDEX 'c1_x y z' ON 'c1'('x y z'); --> p1(b b b)
  }

  6 {
    CREATE TABLE x1(a, b, c, UNIQUE(a, b));
    CREATE TABLE y1(a, b, c, FOREIGN KEY(b, a) REFERENCES x1(a, b));
    CREATE INDEX y1i ON y1(a, c, b);
  } {
    CREATE INDEX 'y1_b_a' ON 'y1'('b', 'a'); --> x1(a,b)
  }

  6 {
    CREATE TABLE x1(a COLLATE nocase, b, UNIQUE(a));
    CREATE TABLE y1(a COLLATE rtrim REFERENCES x1(a));
  } {
    CREATE INDEX 'y1_a' ON 'y1'('a' COLLATE nocase); --> x1(a)
  }

} {
  forcedelete test.db
  sqlite3 db test.db
  execsql $schema

  set expected ""
  foreach line [split $output "\n"] {
    set line [string trim $line]
    if {$line!=""} {
      append expected "$line\n"
    }
  }

  do_test 1.$tn.1 {
    set RES [catchcmd test.db [list .lint fkey-indexes]]
  } [list 0 [string trim $expected]]

  do_test 1.$tn.2 {
    execsql [lindex $RES 1]
    catchcmd test.db [list .lint fkey-indexes]
  } {0 {}}

  db close
}

finish_test