dolphin: Add support for coalesce (#802)

For some reason it's a special case in the AST

Fixes #725

Author: kyleconroy

internal/endtoend/testdata/coalesce/go/db.go renamed to internal/endtoend/testdata/coalesce/mysql/go/db.go

@@ -3,6 +3,7 @@
   "packages": [
     {
       "path": "go",
+      "engine": "mysql",
       "name": "querytest",
       "schema": "query.sql",
       "queries": "query.sql"

internal/endtoend/testdata/coalesce/go/models.go renamed to internal/endtoend/testdata/coalesce/mysql/go/models.go

@@ -0,0 +1,9 @@
+CREATE TABLE foo (bar text, bat text not null);
+
+-- name: Coalesce :many
+SELECT coalesce(bar, '') as login
+FROM foo;
+
+-- name: CoalesceColumns :many
+SELECT bar, bat, coalesce(bar, bat)
+FROM foo;

internal/endtoend/testdata/coalesce/go/query.sql.go renamed to internal/endtoend/testdata/coalesce/mysql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "postgresql",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}