Steps to Reproduce:

@brase have you tried to uninstall and reinstall mssql extension?
@MattIrv could you please investigate what's happening here?
Uninstall -> Reload -> Install -> Reload fixed it.
Thank you!
I'm glad to hear it's working now.
Other users have reported this bug in the past, and suggested it might have something to do with conflicts between other extensions (see https://github.com/Microsoft/vscode-mssql/issues/383) but we've never been able to get a consistent repro for it.
Is there any chance you'd be willing to share a list of your installed extensions so that we can get another data point on this? You should be able to get the list by running code --list-extensions from the Windows command prompt or Powershell.
I just had this issue, fixed in the same way with a reinstall of the extension. Pretty sure it was working when I originally installed it, then after several Code and extension updates it wasn't working today.
Here are the extensions I have installed:
DotJoshJohnson.xml
eriklynd.json-tools
filipw.scriptcsRunner
mohsen1.prettify-json
ms-mssql.mssql
ms-python.python
ms-toolsai.vscode-ai
ms-vscode.azure-account
ms-vscode.csharp
ms-vscode.PowerShell
PeterJausovec.vscode-docker
PKief.material-icon-theme
Sorry, I am a bit late. Here are my installed extensions
2gua.rainbow-brackets
adamvoss.yaml
ban.spellright
codezombiech.gitignore
DavidAnson.vscode-markdownlint
dbaeumer.vscode-eslint
donjayamanne.githistory
DotJoshJohnson.xml
DougFinke.vscode-pandoc
dracula-theme.theme-dracula
EditorConfig.EditorConfig
Equinusocio.vsc-material-theme
espresso3389.genuuid
formulahendry.auto-close-tag
groksrc.ruby
HookyQR.beautify
hoovercj.haskell-linter
Ionide.Ionide-FAKE
Ionide.Ionide-fsharp
Ionide.Ionide-Paket
jcanero.hoogle-vscode
johnpapa.winteriscoming
justusadam.language-haskell
ms-mssql.mssql
ms-vscode.azure-account
ms-vscode.cpptools
ms-vscode.csharp
ms-vscode.PowerShell
msjsdiag.debugger-for-chrome
PeterJausovec.vscode-docker
PKief.material-icon-theme
pprice.better-merge
robinbentley.sass-indented
shardulm94.trailing-spaces
Vans.haskero
vsciot-vscode.vscode-arduino
vscodevim.vim
waderyan.gitblame
I encountered this problem and found this error in dev tools:
[Extension Host] Activating extension `ms-mssql.mssql` failed: Cannot find module 'vscode-nls'
The file that caused it was C:\Users\USERNAME\.vscode\extensions\ms-mssql.mssql-1.2.1\out\src\constants\localizedConstants.js.
Running npm install in the extension folder (C:\Users\USERNAME\.vscode\extensions\ms-mssql.mssql-1.2.1) fixed it for me.
I've got this same issue. I've tried unistalling/reinstalling and disabling all of my other extensions, but I'm still getting the error.
I ended up solving this problem by going into %USERPROFILE%\.vscode\extensions and deleting the ms-mssql folder and reinstalling. I tried uninstalling and reinstalling, but after uninstalling, I would go into the extensions folder and it would still be there.
Agreed, 64 bit is broken, had to reinstall 32 bit version in able to connect to database.
@grothem
Saved my day. Thank you!!!
For those on linux, deleting the mssql folder from /home/.vscode then reinstalling the extension worked for me.
Platform: linux, x86_64, name=ubuntu, version=20.04 (Ubuntu16)
Installing SQL tools service to /home/zakarialhacker/.vscode/extensions/ms-mssql.mssql-1.9.0/sqltoolsservice/1.9.0/Ubuntu16.
Downloading https://download.microsoft.com/download/4/1/c/41ceb814-b8d3-4157-9dd0-b4aa0e11484d/microsoft.sqltools.servicelayer-rhel-x64-netcoreapp2.2.tar.gz
(42606 KB) .................... Done!
Installing ...
Done! 475 files unpacked.
Done
the extension worked for me.
Most helpful comment
Uninstall -> Reload -> Install -> Reload fixed it.
Thank you!