sqlite: separate contains query

Using `select 1` for contains query tells sqlite not to actually load
the data for simple contains queries

eth/db/kvstore_sqlite3.nim

@@ -12,7 +12,7 @@ export kvstore
 type
   SqStoreRef* = ref object of RootObj
     env: ptr sqlite3
-    selectStmt, insertStmt, deleteStmt: ptr sqlite3_stmt
+    getStmt, putStmt, delStmt, containsStmt: ptr sqlite3_stmt
 
 template checkErr(op, cleanup: untyped) =
   if (let v = (op); v != SQLITE_OK):
@@ -26,16 +26,16 @@ proc bindBlob(s: ptr sqlite3_stmt, n: int, blob: openarray[byte]): cint =
   sqlite3_bind_blob(s, n.cint, unsafeAddr blob[0], blob.len.cint, nil)
 
 proc get*(db: SqStoreRef, key: openarray[byte], onData: DataProc): KvResult[bool] =
-  checkErr sqlite3_reset(db.selectStmt)
-  checkErr sqlite3_clear_bindings(db.selectStmt)
-  checkErr bindBlob(db.selectStmt, 1, key)
+  checkErr sqlite3_reset(db.getStmt)
+  checkErr sqlite3_clear_bindings(db.getStmt)
+  checkErr bindBlob(db.getStmt, 1, key)
 
-  let v = sqlite3_step(db.selectStmt)
+  let v = sqlite3_step(db.getStmt)
   case v
   of SQLITE_ROW:
     let
-      p = cast[ptr UncheckedArray[byte]](sqlite3_column_blob(db.selectStmt, 0))
-      l = sqlite3_column_bytes(db.selectStmt, 0)
+      p = cast[ptr UncheckedArray[byte]](sqlite3_column_blob(db.getStmt, 0))
+      l = sqlite3_column_bytes(db.getStmt, 0)
     onData(toOpenArray(p, 0, l-1))
     ok(true)
   of SQLITE_DONE:
@@ -44,44 +44,45 @@ proc get*(db: SqStoreRef, key: openarray[byte], onData: DataProc): KvResult[bool
     err($sqlite3_errstr(v))
 
 proc put*(db: SqStoreRef, key, value: openarray[byte]): KvResult[void] =
-  checkErr sqlite3_reset(db.insertStmt)
-  checkErr sqlite3_clear_bindings(db.insertStmt)
+  checkErr sqlite3_reset(db.putStmt)
+  checkErr sqlite3_clear_bindings(db.putStmt)
 
-  checkErr bindBlob(db.insertStmt, 1, key)
-  checkErr bindBlob(db.insertStmt, 2, value)
+  checkErr bindBlob(db.putStmt, 1, key)
+  checkErr bindBlob(db.putStmt, 2, value)
 
-  if (let v = sqlite3_step(db.insertStmt); v != SQLITE_DONE):
+  if (let v = sqlite3_step(db.putStmt); v != SQLITE_DONE):
     err($sqlite3_errstr(v))
   else:
     ok()
 
 proc contains*(db: SqStoreRef, key: openarray[byte]): KvResult[bool] =
-  checkErr sqlite3_reset(db.selectStmt)
-  checkErr sqlite3_clear_bindings(db.selectStmt)
+  checkErr sqlite3_reset(db.containsStmt)
+  checkErr sqlite3_clear_bindings(db.containsStmt)
 
-  checkErr bindBlob(db.selectStmt, 1, key)
+  checkErr bindBlob(db.containsStmt, 1, key)
 
-  let v = sqlite3_step(db.selectStmt)
+  let v = sqlite3_step(db.containsStmt)
   case v
   of SQLITE_ROW: ok(true)
   of SQLITE_DONE: ok(false)
   else: err($sqlite3_errstr(v))
 
 proc del*(db: SqStoreRef, key: openarray[byte]): KvResult[void] =
-  checkErr sqlite3_reset(db.deleteStmt)
-  checkErr sqlite3_clear_bindings(db.deleteStmt)
+  checkErr sqlite3_reset(db.delStmt)
+  checkErr sqlite3_clear_bindings(db.delStmt)
 
-  checkErr bindBlob(db.deleteStmt, 1, key)
+  checkErr bindBlob(db.delStmt, 1, key)
 
-  if (let v = sqlite3_step(db.deleteStmt); v != SQLITE_DONE):
+  if (let v = sqlite3_step(db.delStmt); v != SQLITE_DONE):
     err($sqlite3_errstr(v))
   else:
     ok()
 
 proc close*(db: SqStoreRef) =
-  discard sqlite3_finalize(db.insertStmt)
-  discard sqlite3_finalize(db.selectStmt)
-  discard sqlite3_finalize(db.deleteStmt)
+  discard sqlite3_finalize(db.putStmt)
+  discard sqlite3_finalize(db.getStmt)
+  discard sqlite3_finalize(db.delStmt)
+  discard sqlite3_finalize(db.containsStmt)
 
   discard sqlite3_close(db.env)
 
@@ -142,17 +143,22 @@ proc init*(
   """
 
   let
-    selectStmt = prepare "SELECT value FROM kvstore WHERE key = ?;":
+    getStmt = prepare "SELECT value FROM kvstore WHERE key = ?;":
       discard
-    insertStmt = prepare "INSERT OR REPLACE INTO kvstore(key, value) VALUES (?, ?);":
-      discard sqlite3_finalize(selectStmt)
-    deleteStmt = prepare "DELETE FROM kvstore WHERE key = ?;":
-      discard sqlite3_finalize(selectStmt)
-      discard sqlite3_finalize(insertStmt)
+    putStmt = prepare "INSERT OR REPLACE INTO kvstore(key, value) VALUES (?, ?);":
+      discard sqlite3_finalize(getStmt)
+    delStmt = prepare "DELETE FROM kvstore WHERE key = ?;":
+      discard sqlite3_finalize(getStmt)
+      discard sqlite3_finalize(putStmt)
+    containsStmt = prepare "SELECT 1 FROM kvstore WHERE key = ?;":
+      discard sqlite3_finalize(getStmt)
+      discard sqlite3_finalize(putStmt)
+      discard sqlite3_finalize(delStmt)
 
   ok(SqStoreRef(
     env: env,
-    selectStmt: selectStmt,
-    insertStmt: insertStmt,
-    deleteStmt: deleteStmt
+    getStmt: getStmt,
+    putStmt: putStmt,
+    delStmt: delStmt,
+    containsStmt: containsStmt
   ))