sqlite - how do I get a one row result back? (luaSQLite3)

Question

How can I get a single row result (e.g. in form of a table/array) back from a sql statement. Using Lua Sqlite (LuaSQLite3). For example this one:

SELECT * FROM sqlite_master WHERE name ='myTable';

So far I note:

• using "nrows"/"rows" it gives an iterator back
• using "exec" it doesn't seem to give a result back(?)

Specific questions are then:

Q1 - How to get a single row (say first row) result back?

Q2 - How to get row count? (e.g. num_rows_returned = db:XXXX(sql))

Answer 1

Here is a demo of getting the returned count:

> require "lsqlite3"
> db = sqlite3.open":memory:"
> db:exec "create table foo (x,y,z);"
> for x in db:urows "select count(*) from foo" do print(x) end
0
> db:exec "insert into foo values (10,11,12);"
> for x in db:urows "select count(*) from foo" do print(x) end
1
> 

Answer 2

In order to get a single row use the db:first_row method. Like so.

row = db:first_row("SELECT `id` FROM `table`")
print(row.id)

In order to get the row count use the SQL COUNT statement. Like so.

row = db:first_row("SELECT COUNT(`id`) AS count FROM `table`")
print(row.count)

EDIT: Ah, sorry for that. Here are some methods that should work.

You can also use db:nrows. Like so.

rows = db:nrows("SELECT `id` FROM `table`")
row = rows[1]
print(row.id)

We can also modify this to get the number of rows.

rows = db:nrows("SELECT COUNT(`id`) AS count FROM `table`")
row = rows[1]
print(row.count)

Answer 3

Just loop over the iterator you get back from the rows or whichever function you use. Except you put a break at the end, so you only iterate once.

Getting the count is all about using SQL. You compute it with the SELECT statement:

SELECT count(*) FROM ...

This will return one row containing a single value: the number of rows in the query.

Answer 4

This is similar to what I'm using in my project and works well for me.

local query = "SELECT content FROM playerData WHERE name = 'myTable' LIMIT 1"

local queryResultTable = {}

local queryFunction = function(userData, numberOfColumns, columnValues, columnTitles)

    for i = 1, numberOfColumns do

        queryResultTable[columnTitles[i]] = columnValues[i]

    end

end

db:exec(query, queryFunction)

for k,v in pairs(queryResultTable) do

    print(k,v)

end

You can even concatenate values into the query to place inside a generic method/function.

local query = "SELECT * FROM ZQuestionTable WHERE ConceptNumber = "..conceptNumber.." AND QuestionNumber = "..questionNumber.." LIMIT 1"