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We present the results of a search for damped Lyman-alpha (DLA) systems inthe Sloan Digital Sky Survey II (SDSS), Data Release 7. We use a fullyautomatic procedure to identify DLAs and derive their column densities. Theprocedure is checked against the results of previous searches for DLAs in SDSS.We discuss the agreements and differences and show the robustness of ourprocedure. For each system, we obtain an accurate measurement of the absorber'sredshift, the HI column density and the equivalent width of associated metalabsorption lines, without any human intervention. We find 1426 absorbers with2.15 < z < 5.2 with log N(HI)>=20, out of which 937 systems have log N(HI)>=20.3. This is the largest DLA sample ever built, made available to thescientific community through the electronic version of this paper. In thecourse of the survey, we discovered the intervening DLA with highest HI columndensity known to date with log N(HI)=22.0+/-0.1. This single system provides astrong constraint on the high-end of the N(HI) frequency distribution nowmeasured with high accuracy. We show that the presence of a DLA at the blue endof a QSO spectrum can lead to important systematic errors and propose a methodto avoid them. This has important consequences for the measurement of thecosmological mass density of neutral gas at z~2.2 and therefore on ourunderstanding of galaxy evolution over the past 10 billion years. [truncated]

Evolution of the cosmological mass density of neutral gas from Sloan Digital Sky Survey II - Data Release 7