Viable alternatives to SQL?

Many sites let you search databases of information, but the search
queries are very limited.

I'm creating a site that'll allow arbitrary SQL queries to my data (I
realize I'll need to handle injection attacks).

Are there other viable ways to query data? I read a little on
"Business System 12" (BS12), Tutorial D, and even something called
T-SQL (I think), but they all seem theoretical and not fully
implemented.

I want a query language that non-techies can use easily, but also
supports arbitrarily complex queries. Does such a language exist?

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