print(date('now','start of year','+9 months','weekday 2'))

gmod_sqldatetime.lua

-- http://www.sqlite.org/lang_corefunc.html#last_insert_rowid
function sql.LastRowID()
	local ret = sql.Query("SELECT last_insert_rowid() as x")[1].x
	return ret
end


-- http://www.tutorialspoint.com/sqlite/sqlite_date_time.htm
local escape=sql.SQLStr
local function gen_datefunc(fname)
	local beginning = "SELECT "..fname.."("
	local function func(...)
		
		local mods = {...}
		for k,v in next,mods do
			mods[k]=isnumber(v) and v or escape(v)
		end
		local q=beginning..table.concat(mods,",")..") as x;"

		local ret = sql.Query(q)
		ret = ret and ret[1]
		ret = ret and ret.x
		ret = ret and ret~="NULL" and ret 
		
		return ret
		
	end
	
	sql[fname]=func
	_G[fname]=func
end

gen_datefunc'date'
gen_datefunc'time'
gen_datefunc'datetime'
gen_datefunc'julianday'
gen_datefunc'strftime'

print(date('now','start of year','+9 months','weekday 2'))
print(julianday('now'))
print(time('12:00', 'localtime'))
print(time('12:00', 'utc'))
	
	
	
-- Example command: sql .tables
-- Return serverside data by calling with: cmd sql .tables
local commands={
	tables="SELECT name FROM sqlite_master WHERE type='table'"
}
concommand.Add("sql",function(pl,_,_,line)
	if SERVER and pl:IsValid() and not pl:IsSuperAdmin() then return end
	local function out(...)
		if SERVER and pl and pl:IsValid() then
			pl:ChatPrint(table.concat({"SQL>",...}," "))
		else
			Msg"[SQL] " print(...)
		end
	end
	local cmd,arg = line:match'^%.(%w+) (.*)$'
	if not arg then
		cmd = line:match'^%.(%w+)$'
	end
	if cmd then
		cmd=commands[cmd]
		if not cmd then out"Unknown command" return end
		if isfunction(cmd) then
			cmd=cmd(arg,line)
			if not cmd then return end
		end
		line=cmd
	end
	
	local ret = sql.Query(line..';')
	if ret == false then
		out("Error: "..tostring(sql.LastError()))
	elseif ret==nil then
		out"Command executed succesfully"
	elseif not istable(ret) then
		out("Unhandled value: "..tostring(ret))
	elseif not next(ret) then
		out"Empty result set returne"
	else 
		out ("Query results: "..table.Count(ret))
		for k,v in next,ret do
			if k>50 then
				out"--- truncated ---"
				break
			end
			local t={}
			for kk,vv in next,v do
				t[#t+1] = string.format("%s = %s",kk,isstring(vv) and  tonumber(vv) and vv or ("%q"):format(vv) or tostring(vv))
			end
			out(table.concat(t,"  "))
		end
	end
end)